THE BLUES ON A RAINY NIGHT
On the Rocks
The Woodstock Times
Nov. 21, 1996
This is an old one, from my first year at the Woodstock Times. This column has been adapted for several editions of “The Catskills: a geological Guide.”
“Carved in stone” is a common enough cliché. Its meaning is plain enough: any concept etched in stone is permanent, it will never go away or be altered. There is an important implication in the term; something carved in stone must be of some real importance. Otherwise – who would bother?
To a geologist things carved in stone are much more commonplace. Lots of things are carved in stone. Some of the most mundane events have, by happenstance, been recorded not by a skilled engraver, but by the everyday events of nature. If you know what to look for, sometimes the rocks light up with unexpected etchings.
You have, no doubt, commonly walked the sidewalks on a rainy night. To the young and in love it can be a great pleasure; to most of the rest of us it’s just cold and wet. But, in the Catskills, a dark, rainy night can bring a journey into the past. You see, most of our Catskill villages still have a lot of old bluestone sidewalks, and each old slab can be a time machine.
Bluestone has long been quarried in the Catskills. This durable and attractive stone holds up very well to the traffic of feet. It was deposited nearly 400 million years ago mostly near the coastline of the ancient Catskill Sea. Its sands once traveled down the rivers of the Catskill Delta and came to be deposited as flat sheets on the shallow sea floors or within the river channels themselves. With time came hardening and then lithification. With a lot more time came quarrymen to chisel out these stones and cut them into sidewalk slabs. Now they line our streets, but they often still retain vestiges of their venerable past.
Go out, find some bluestone walks, and really take a look at them. Most Woodstock sidewalks are now of concrete, but there still are some old bluestone slabs. Look at the sidewalk along the cemetery on Rock City Road, and on Tinker Street near Maple Ave. Look also at the stones leading to people’s front doors. Many are featureless, but many others display sedimentary structures which take us back to moments of time in the Devonian.
Look for two of these structures. The first is the most obvious; these are the ripple marks. Devonian age currents passed across these Devonian sands and sculpted them into the delicate ripples. Often the ripples are steeper on one side. That steep side is inclined toward the direction the current was flowing. It is a most remarkable experience to visualize these briefest and most ephemeral events of so long ago. They should not exist. How could such delicate structures survive long enough to turn into stone? And yet, there they are. Were these currents of any importance? Not at all; they were just the most everyday of events and yet they are “carved in stone.”
Bluestone slab with ripple marks
The other structure is the flow lineation. Again as currents sweep across sea floors or stream bottoms they sculpt the sand. This time the resulting feature is virtually invisible. The grains are lined up into a subtle lineation which only appears millions of years later when the stone cutter splits the rock. The resulting fracture has a faint lineation to it.
Bluestone slab with flow lineations, oriented lower right to upper left
Both of these features are quite clear in broad daylight and not much harder to see at night, under street lights. But on a rainy night, when the street lights are reflected off the wet sidewalks, these features light up. They are almost electric. It’s something to look for anywhere there are bluestones, which is all of eastern North America. I found a lot of flow lineations on the bluestones of Woodstock, but only one good ripple marked slab. That was on the first place I looked: the doorstep of Woodstock Wine and Liquors.
So you don’t have to be young and in love to enjoy a walk on a dark rainy night. Ripple marks and flow lineations are nice too, although they do come in a distant second place.
March 14th, the year 387,469,184 BC, late afternoon
All day long, very moist air has been rising up the slopes of the Acadian Mountains, and this has triggered a series of severe thunderstorms. Dark banks of towering storm clouds rise above the 32,000-foot-tall mountain peaks. A great col lies between two adjacent summits, and this forms a huge geographic bowl. Three closely spaced lines of thunderstorms have unloaded, in quick succession, upon this vicinity, and the rains have flooded the bowl. The rain of the first line of storms quickly waterlogged the soils and the subsequent torrents have raced off downhill in deep, fast-flowing erosive streams. Deep gullies have been rapidly cut into the soft, blue-black upper slopes of the bowl. Vast amounts of sediment have been mobilized and a thick ooze of dirty water (in fact, almost watery dirt) has funneled into gullies too numerous to count. Downslope, the gullies combine into several powerful cascading streams. The flows are now too great to be accommodated by the temporary channels they have cut, and so the deep channels are being widened rapidly. More dark earth is engulfed by the erosive powers of the expanding flows, and whole earthen slopes crash down into the torrent. The rush of the confined water is being pushed and hurried along by the great amounts of water backed up behind.
From various compass points, similar flows combine to a point well down on the face of the Acadian massif. Here, today’s cascade, and many earlier ones like it, have combined to carve a great vee-shaped cleft in the mountain range. This gap dwarfs the canyons above it. Through this cleft, on this day, flow several large Niagara’s; this is a catastrophic event, a thousand year flood.
Below these narrows, the Acadian slopes level out. Vast piles of coarse sand and gravel have formed an enormous, rounded apron of sediment, draped against the slopes of the Acadians. As it flows across this slope, the water breaks up into a number of smaller streams, which continue several miles down the gentle slope until a level nearly that of the sea is reached. At sea level, the streams enter a broad, flat delta top landscape, which is a morass of flooded bayous, marshes and ponds.
The drainage of the Acadian slopes thus forms a great hourglass, and this whole drainage system functions as a giant mountain-destroying machine. The upper basin makes up the wide top of the glass where the rain water is gathered. As it cascades down the slope, it erodes into the mountainous landscape. Below, the narrows make up the constricted middle of the hourglass; here the flow is most effective, and water with its burden of sediment is efficiently transported away from the mountain. The gentle slopes reach down to the flat morass that makes up the bottom of the hourglass. This is where all the material eroded from above ends up.
The morass I speak of makes up the great Catskill Delta. Now, its various glutted and disorganized channels of water make their ways toward the sea. These channels are not nearly large enough to hold the water, and they are in full flood. The blue-black floodwater streams have fanned out across the delta plain. Much of the foliage that had grown along the streams has been swept away. Beyond the now-submerged stream channels, the flood currents slow down and the sediments begin to be deposited as dark horizons of muddy sand. Many plants are being buried within these sands; those that had hung on against the currents are being buried in an upright, standing position.
Meanwhile the main flow continues down the channels of the delta. Downstream, the flow is still rapid, but it is beginning to ebb. Colonies of river-dwelling clams are overwhelmed and are quickly buried by masses of sand. These clams have little to fear; muscular and active burrowers, they will not remain buried for long. At the mouths of the Catskill Delta rivers, the waters, dark with sand and silt, are being disgorged into the western Catskill Sea. From above, large plumes of dirty water can be seen slowly expanding out into the sea. Many tree trunks and a flotsam of broken foliage drift seaward, half hidden in the dark plumes.
By midnight the storms have long been over. The skies are clear and the stars shine, competing with a wine-colored moon. The upper slopes of the Acadian Mountains are now dark and silent. Further downstream, the churning flows of the day are still rapid and gurgling with noise, but the normal languid flow of the delta will soon return. The rivers are still dirty, but they are clearing. Offshore the plumes of sediment are settling into thick strata of sticky sand. A large number of shellfish are dying in that burial; they are the ones which cannot burrow to safety. Their shells will lie, buried as fossils, for at least 400 million years.
It has been a very hard day for the biota of the Catskill Delta. But nobody cares. The world of the Devonian is a soul-less one; there is no mourning, no grief, no pity or even self-pity. Indeed, there is no real understanding of exactly what happened today, and by midnight, there are few living creatures who can even remember these terrible events.
Overnight, the currents will slow down enough so that horizontal horizons of sand will accumulate across large expanses of river bottom and seafloor. These deposits will become bluestone.
Up river, the first of many freshwater clams is emerging from the sands, having escaped its entombment. Life goes on.
Those bluestone sidewalks
Windows Through Time
July 2nd, 2009
We rarely pay sufficient attention to the very greatest emblems of our history, in time to save them from destruction. The old covered bridges were replaced by modern spans and, not until only a few were left, did anyone bother to care. By then it was nearly too late, but a few were saved and are still to be seen. All across the land, beautiful old barns have been left to decay and fall down. Today you can actually see signs along the highways, posted by people who wish to buy old barns and tear them down to salvage and sell their wood. It’s such a shame. I fear that nobody will do anything until just a handful of barns are left.
There’s another emblem of the past that I seem to find myself alone in worrying about. That is the bluestone sidewalk. We see them all over the place, but they are being replaced by cement and that has been the case for a long time. Many are still there, but for how long?
Old bluestone sidewalk
If you care to take notice, they can be seen. There are several of them in my town of Freehold. I still see some in Oneonta where I teach. The city of Hudson has some and so on. They are old; they were installed a long time ago, and they are showing their age.
But just what is bluestone? That, of course, is something any local geologist will know about, and I am no exception. Bluestone is a type of sandstone and thus (guess what?) it is composed of sand. It is quartz sand as a matter of fact. So, where did all that sand come from?
Much of Catskill sandstone was originally formed as sediment in the channels of ancient rivers. There were a lot of rivers around here during the Devonian time period and so there is a lot of sandstone. When it has just the right amount of the mineral called feldspar in it, then the sandstone takes on a vaguely blue appearance and, presto, it is bluestone.
Those Devonian age rivers sometimes had powerful flows of water within them. These currents swept along large masses of sand. We are probably talking about Devonian age flood events. At the peak of a flood, the currents were powerful and dirty with sand and silt. But floods don’t last forever; they do abate. As the currents, once again, slowed down, they could no longer continue to transport their load of sand. Most of it had to be deposited. At exactly the right current speed, sand is deposited in thin, very flat sheets. These strata are the ancestors of sidewalks.
The horizontally laminated rock that results is well-suited for splitting. Long ago quarrymen learned how to do this, and they became very skilled at splitting and cutting the rock into slabs just the right size to make sidewalks. It was backbreaking work; I hate to think how hard it must have been. But, the pay was pretty good by the standards of the 19th Century, and so many were attracted to the work. Good bluestone quarries sprang up in the Hudson Valley, west of the river. Then more were opened up in the eastern Catskills. You can still see the old, now abandoned quarries; they are common
View of an old bluestone quarry
The earliest quarries eventually played out and were abandoned. The industry has slowly migrated westward across the Catskills, and now it’s centered in the vicinity of the Delaware River. People still produce very good bluestone out there.
The rock is found all over the world, but the best bluestone comes from the Catskills. Our stone is enormously resistant to weathering, and that is why it made such good sidewalks. The rock doesn’t become very slippery when wet and that helps too. Blocks of it, cut a century ago, have had people walking across them for all that time and they often show little wear from all the abuse. But, they are getting old. It’s the corners that go first. Weathering works in from both sides of a corner and gradually decomposes it. Then, commonly, stresses build up within the stone, resulting in its cracking. That hurries things along quite a bit.
So, sadly, town fathers look at their old sidewalks, and decide they have to go. They come to be replaced, usually by cheaper cement. There is probably little that can be done to stop or even slow this, but it is sad. Still, we should appreciate this fine old stone, and we owe it to ourselves to be a little more aware of these sidewalks when we see them. They are part of our heritage and a very important part of it. You can tell your grandchildren about them. And tell me too, if there are good bluestone sidewalks near you. Contact the author at email@example.com
Joints on the Wall of Manitou
Windows Through Time
Robert and Johanna Titus
Three weeks ago this blog was about the Wall of Manitou. We wrote about its origins but, ever so coyly; we were not very specific in this. The wall is ten miles long, straight as an arrow and that arrow has a compass direction of south-30 degrees west.
Satellite image of the Wall of Manitou.
And two week ago our blog described long straight fracture patterns called joints. They are very frequent throughout the Catskills and, remarkably, most of the time, they also have compass directions of south–30 degrees west. This was a hint, a big one. Did you pick up on that? There is a story here. Those joint fractures and the Wall of Manitou have too much in common for it to be an accident. There must be some sort of a relationship. Well, there is.
We hope you remember that joints form when great masses of rock are compressed, usually during great mountain building events. The compression does not actually fracture the rock, that happens later in time, when the stress ends and the rocks “relax.” Our Catskills joints compressed sometime after 400 million years ago. Something you would likely call Europe had collided with North America and that collision resulted in the rising of mountain ranges throughout all of New England. Geologists call them the Acadian Mountains. If you keep reading this blog you will hear a lot more about these mountains. Anyway, that massive collision compressed rocks throughout New York State, especially the Catskills
The collision of “Europe” with North America and the resulting Acadian Mountains. See NE/SW orientation.
A long time after the uplift of these mountains, Europe broke free from North America and drifted back off to the east, leaving a growing Atlantic Ocean behind. That split was about 200 million years ago. And that was when all the relaxation occurred and that is also when all those joint fractures came into existence. Joints always form perpendicular to the maximum relaxation stresses. These maximum stresses, as it happened, were northwest to southeast. So the joints formed northeast to southwest, just what we see (We are ignoring secondary joints at a 90 degree angle to the primary ones).
Did you follow all that? Europe collided with North America, compressed North American rocks and, when Europe drifted away to the southeast, all those joints formed. Well, what does any of this have to do with the Wall of Manitou?
It has, in fact, everything to do with it. Perhaps you might like to hike the Blue Trail, north from North Lake. Along the way, here and there, you will find northeast/southwest trending joints. There are a lot of them.
Hikers stand upon Blue Trail joints.
It must have been just like that during the Ice Age. During parts of the Ice Age the Hudson Valley was filled with ice, right to the top. And that ice was moving. It formed a great stream of ice, ever so slowly flowing down the valley, and of course, rubbing up against the Catskill Front.
Here’s where it gets interesting. Ice, when in tight contact with bedrock, forms a bond with the rock. In simple terms, the ice sticks to the rock. Did you ever stick your tongue to the bottom of an ice tray when you were a kid? Well, then you know exactly how sticky ice can be. That happened to bedrock along the Wall of Manitou, during much of the Ice Age.
Well, when enough of a tug was generated, the moving ice would, from time to time, yank huge masses of rock loose. And – you guessed it – those joint fractures proved to be weak points where the breaks could most easily occur. Had you been to North Lake way back then, you would have heard, sporadically, great echoing cracking sounds. Each would mark the breaking of a mass of rock off of the growing Wall of Manitou. Almost always, those fractures had a northeast to southwest orientation.
Over long periods of time – and this is geology; we always have long periods of time – the Wall of Manitou came to be shaped and steepened into what it is today. All the action was occurring out of sight, beneath the surface of the Hudson Valley glacier. Today, the great Wall rises about 2000 feet above the floor of the valley. And it does something that most slopes don’t do. It steepens toward the top. That’s one good reason why it is such a scenic feature.
When we stand at the edge of the Catskill Mountain House ledge, we always look out at the valley before us and we always see it filled to the top by a glacier. The ice slowly moves by us, headed south. And every so often, we do hear those ear splitting cracks, generated by masses of rock breaking free and being dragged off by the advancing glacier. Then our mind’s eyes watch as the ice begins to melt away. The ice shrinks away from the ledge and reveals nature’s ice age handiwork. That Wall of Manitou rises out of the melting glacier. It is a marvelous revelation.
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A Petrified Delta
Windows Through Time
June 26th 2009
The Catskills present a number of public images. To many they are the land of Rip Van Winkle. We, in the Catskills, love the old story and retell it often. The plot seems to have been set right here on the Catskill Front. Other people immediately conjure up images of Borsch Belt hotels with their stand up comics. Then there are the images that were painted by the artists of the Hudson River School of Art. It really was here, in our Catskills, that a deep, artistic appreciation of a “sublime” landscape was born. We are all enriched by that view. Closely related to this is the great outdoors image of the Catskills, something that appeals to nearly everybody. Much of the spiritual side of what we call environmentalism comes from places like our Catskills.
But to geologists there is an altogether different concept of the Catskills. Not better, not worse, but very, very different! You see, there are thousands of feet of sedimentary rocks that make up the Catskill Mountains. It is mostly sandstone, along with a fair amount of shale. Throughout this vast thickness we find sedimentary features that we can identify. These reveal ancient environments petrified in the strata. They are fragments of ancient landscapes that have hardened into rock. We see original deposits with their original structures, and we can put names on them.
There are for example, throughout the Catskills, cross sections of ancient river channels. There are the deposits of old floodplains. We find ancient ponds and swamps. And so on. And when I say ancient I am not kidding around. These rocks range from more than 400 million years in age to about 350. That places them all in a time period that we call the Devonian.
Outlines of cross sections of Devonian stream channels at Plattekill Falls.
All of these petrified Devonian environments are typical of a great river delta. And again, I am not kidding around. These delta deposits are thousands of feet thick and stretch from the Catskill Front, in the Hudson Valley, to at least western New York State and probably a lot farther. That’s big!
All this has a name; it is called the Catskill Delta. Some would call it the Catskill delta complex. The latter emphasize that these delta deposits stretch for hundreds of miles south through the whole Appalachian realm. They have a point. This is not just a single delta, but a long complex of many deltas.
How did they form? Well, one thing is certain: every delta consists of heaps of sediment that were deposited when a river, big or small, flowed into a standing body of water, again big or small. Really big deltas form at the ends of really big rivers. The Mississippi River has a large delta. The Nile Delta is at the end of an equally long and large river.
But, you might ask “There are two problems: where did the really big rivers go? And, by the way, where is the body of water that it flowed into?” Those are good questions and they deserve, actually they demand answers.
Where did the rivers go? Well, that gets us to all that sediment. Big deltas need big sources for all their sand, silt and clay. The Mississippi has most of North America; the Nile has much of Africa. But back in the Devonian, North America was not very big and it could not provide much sediment. Instead our river, or rivers, flowed down the slopes of a great range of mountains, lying in today’s New England. These, called the Acadian Mountains, had, in fact, many streams flowing down their western slopes. All of them carried sediment out onto the great Catskill Delta. Those mountains eroded away long ago and their rivers are gone too.
Map of Acadian Mountains with delta rivers flowing off to the north.
. But what about that standing body of water? Where is that? The rivers of the Catskill Delta flowed across it and then entered something called the “Catskill Sea.” This is where it all gets very surprising. The Catskill Sea was a shallow ocean that stretched clear across all of North America. Beyond North America it merged with something that we would probably want to call the Devonian Pacific Ocean. In short, North America was a breathtakingly different place back in the Devonian.
All this gets us back to my original point. When a geologist has a good view of the Catskills, say from across the Hudson River, then what he or she looks at is a scenic range of mountains. What we actually see, however, is very different. We look up at the Catskills and see a petrified delta. If we could, we would treat it like
Petrified delta, viewed from Greene County. Rte. 81.
so many other specimens we find in the field. We would chisel it loose and bring it back to a museum. We would find a cabinet with a drawer labeled “fossil deltas.” We would put it in that drawer and keep it.
But it is too big for that. Better to enjoy it as it is!
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Fractures from the distant past.
Windows Through Time
Joints just below the Bridge
There is a fine outcropping of Devonian age sandstone all along Catskill Creek, both upstream and downstream from the bridge. That, by itself, would make a good story but there is something else. I noticed some prominent, long straight fractures in the rock. These fractures would, of course, take me through another window of time. These are just below the downstream side of the bridge.
Not all rock fractures are as straight and parallel as these, so I became curious. I climbed down to the outcrop and took a measurement of their compass directions (a well-armed geologist always has a compass handy). I was not the least bit surprised with the results. As I expected, I found a bearing of south, 30 degrees west, a nice almost northeast to southwest orientation. That, I knew, is very common pattern to see throughout all of the Hudson Valley and Catskills. It’s what we found in last week’s blog. I had better do some explaining.
There are fractures and then there are fractures. Most are irregular; the rocks break up into more-or-less random and erratic patterns. But, as I had noticed, the ones at the Durham Bridge were altogether different. They were, all three of them, straight as arrows and perfectly parallel to each other. There was a very clear pattern here.
When Nature puts a pattern in front of a scientist she is challenging him to figure it out. Patterns need to be explained. And the best explanations, when we come up with them, are called theories. Geologists, very long ago, came up with good theory to explain what I was seeing beneath the Durham Bridge. These special fractures are called joints. Joints are just what we have seen here; they are straight, parallel fractures of the rock. But how did they form? That’s the theory part.
Joints record chapters in the tectonic history of a region. They began to form when the rocks, long ago, came to be compressed. It may be hard to imagine that rocks can be squeezed, but they can. That requires immense pressures, but such pressures do occur within the Earth’s crust – deep within the crust.
Now the funny thing about all this is that rocks do not fracture when they are compressed; they have enough give to absorb that stress. But compression does not last forever; it eventually does end, rocks expand, and that is when the fracturing begins. There is a sort of relaxation which occurs as the pressure comes off. At that moment we find that rocks are brittle and it is exactly then that they crack to form joints. So, what triggered all this? We need more theory.
Cycles of compression and relaxation, strong enough to deform and then fracture rocks, can only be associated with the truly great tectonic events. These are not just run of the mill earthquakes; these are the towering mountain building events. And the one which triggered our Catskill Creek joints was one of the biggest mountain building events ever; it made the northern Appalachians. These joints record the collision of something you might call Europe with North America.
That resulted in early uplift in the Northern Appalachians of New England. Compression occurred when the collision occurred. Much later in time, Europe split from North America and drifted away. That’s when the relaxation occurred and then the joints formed.
So my bike ride across the Durham Bridge turned into quite the journey into the past. I gazed at those joints and recognized that they were taking back into time. I was looking at fractures that dated hundreds of millions of years into the past. Now I gazed upwards towards the eastern horizon. In my mind’s eye I saw very tall mountains on that horizon. They were white with snow at their peaks. They have a name; they are called the Acadian Mountains. These had started forming nearly 400 million years ago and had largely eroded away by about 300 million years ago. Those joint fractures that had caught my attention have been here for much of that time.
There is nothing unique about the joints at the Durham Bridge. It is quite likely that there are many similar joints near where you live. These are features that people tend not to notice until they develop trained eyes. Well, you have just trained your eyes! Please look carefully at rock outcroppings in your neck of the woods. Look for long straight fractures, often with smooth flat surfaces. These are the joints in your neighborhood. Reach the author at firstname.lastname@example.org
The Wall of Manitou
Windows Through Time
A few years ago we celebrated the Quadricentennial of Henry Hudson’s 1609 exploration of the Hudson River this year. It is an important landmark. Hudson made the first serious European exploration of the valley and its river. I am guessing that it must have been an especially fascinating moment for Hudson and his crew when they first spied the tall, blue silhouette of the Catskill Mountains as they were sailing north. They must have wondered about those mountains as the sailed past them. They would never get to go up there. We can.
Satellite view of Catskill front
This is the Catskill Front, or if you like, the Wall of Manitou, very roughly the Algonquian words for the Wall of God. It is a very striking landscape feature; stretching about ten miles long and extending from Overlook Mountain, in the south, to North Point, in the north. It is broken twice by sizable cloves. The biggest is Kaaterskill Clove; the other is Plattekill Clove and that is only a bit smaller of the two. You can hike most of the Catskill Front on the Escarpment Trail. That long hike will take you past many very nice views. The hike is a big investment of time, but well worth the effort.
Walking the Catskill Front is one way of enjoying it. The other is to go down into the Hudson Valley and look up at it. Most of us have gazed at this scenic profile of the Catskills. Many of us have favorite vantage points. Mine is from the south porch of artist Frederic Church’s mansion, Olana. There, the mountains never look exactly the same, no matter how many times you visit. There are the winter and summer views, of course. But then there are bright and sunny days when the mountains positively gleam, and also dark days when the mountains are enshrouded in low lying cloud banks. To watch as thunderstorms pass over the Catskills is a grand experience. I think that they must have invented thunderstorms just for the Catskills. On clear dry days at Olana, the image of the mountains seems to expand; I think that the dry air actually magnifies the view. It is always a wonderful panorama at Olana. Church and his family enjoyed it for decades; I envy them that.
View of Catskill Front from Olana
To a geologist there are other wonders to the Catskill Front. It has had its mysteries for us. We enjoy its natural beauty, but we also ask questions about it. One of them is “Why is it there.” There is a passage from an article by the late Dr. John Rodgers, a very well respected geology professor from Yale University. He placed himself on the Mountain House ledge, gazing eastward into the Hudson Valley, and simply marveled and wondered as to its very existence. How had it formed? He had many ideas but he did not really know for sure.
The questioning was pertinent. The Mountain House ledge lies at the top of many thousands of feet of sedimentary rock: called the Catskill sequence. Where did it all come from? The sequence thins to the west, but it extends all the way past the Mississippi River; that is a lot of sediment! It was famed 19th Century Albany geologist James Hall who first recognized this. But, he wondered, where did all this sediment come from? He looked eastward, like John Rodgers, and he too could not answer the question. There should have been a great source of sediment out there in the east, but he did not see it.
Another very puzzling question has long been “Why is the Catskill Front so straight.” And indeed, through all of that length, it is most remarkably straight. How could that be? Nature is not too fond of straight lines; she only uses them for the best of reasons. She much prefers random lines. Not here. Why not?
And then there is the direction of that straight line. The Wall of Manitou runs approximate south, 30 degrees west. That is a commonly observed compass direction throughout our region. And, again, the question is why?
My column, this week, is, of course, a teaser. I can answer these questions, I think. And I will over time. But, I guess that my main point here today to illustrate something essential about scientists. We enjoy good scenery as much as anyone else. But, we scientists do look more deeply into the very nature of Nature and we ask so many questions of Her. It is one thing to enjoy the scenery; it is another thing to understand it. Seeking to understand is just our scientific nature. And that is what we have only just begun today.
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Flocks of geologists
Windows Through Time
June 4, 2009
Dear Dr. Titus – I have been enjoying your columns in the Hudson-Catskill newspapers. I have a question. I wonder what so many college groups have been studying at the Leeds exit along Rt. 23? – WJM – Athens
WJM: Thanks for the good question. Over the years I have heard this one from a lot of people. Anybody who frequently drives this stretch of the road in the autumn or the spring will have seen sometimes large groups of college students climbing over the rocks at this site. You will be interested to know that this is one of the great “geological tourist traps” of the American northeast. Any eastern geologist who is anybody in geology has been to this location. I wonder if I even know any geologist who has not been here. So, what is the big draw?
The answer is that this outcropping displays something called an “angular unconformity,” and this one is a very historic structure. Read on and learn about this peculiar feature. If you are going by sometime soon, you might want to stop and see for yourself that which captivates so many young geologists. If you do, you will see some interesting geology.
The right (east) side of the outcrop displays what are called stratified sedimentary rocks. These are thick horizons of alternating gray sandstone and black shale. Each layer of rock was once located at the bottom of the sea. Back then, these were horizons of sand and mud. That’s a most surprising observation. Look around. Do you see and salt water here? This does not look like the bottom of an ocean, but it once was. That’s incredible but true.
It has been a very long time since the earliest geologists figured this out. So long that we have forgotten who first made this amazing deduction. That’s too bad, because this was not only one of the most important discoveries in the history of geology but of science itself. Look around and think about it. You are standing at what really was the bottom of a sea. These strata of sand and mud formed on that long-ago seafloor. Times have changed!
But there is something else here and it is also important. Notice that the sandstone and shale strata are tilted, they are nearly vertical. When sediments are deposited on the floor of an ocean they are laid down in horizontal sheets. These strata should have stayed that way, but that is not the case here. Again they are nearly vertical. They must have come to be tilted and that’s where the story gets even more interesting. Think about how heavy these rocks are and how much energy it would take to tilt them. The only processes that can lift and tilt such rocks are those of mountain building events.
These rocks are from something called the Ordovician time period; they are about 450 million years old. That’s when North American was enduring a great collision with an eastern landmass much the size of today’s Japan. You would call it Europe or – better – proto-Europe. Collisions, of this sort, initiate chapters of downwarping. The crust folds downward and the seas flood the region. Those seas accumulated the sand and mud that hardened into today’s rocks. Then continued collision came to reverse the whole process and caused a massive mountain building uplift. All this is how those rocks formed, and how they were tilted and raised to above sea level. But, of course, there is still more.
The rocks on the left (west) side of the outcrop are limestones. They formed during a time that is called the Devonian Period and they are only about 400 million years old. They formed in a shallow tropical sea and the rocks are sometimes rich in marine fossils. If you stop here, perhaps you can find a few. This was the bottom of a second ocean!
These too are stratified, but these strata dip to the left. Once again, North America was enduring a collision with another Japan-sized land mass. It was déjà vu all over again! Once again, the crust was folded downwards and that is when the limestone formed. That downwarping would eventually be followed by another uplift. That’s when the tilting occurred.
The boundary between these two units of rock is the part we call an angular unconformity. It represents a period of erosion that followed the first mountain building event and preceded the second.
And that is the centerpiece of what we, and all those college students, are looking at. This is a petrified record of two mountain building events. There is a lot of history here and young geologists come from all over to see it. You can too. Contact the author at firstname.lastname@example.org
A voyage of the mind, a voyage to a lake
Windows Through Time – May 21, 2009
We are the mind’s eye, the human imagination, and we are drifting high across the Hudson Valley’s sky, exactly 14,000 years ago. Our present location is northeast of Chatham in the middle Hudson Valley. Below us should be Kinderhook Creek and indeed, way down there we can see a fine flow of water but something is dreadfully wrong. We drop down to get a better look. Stretching behind us, to the northeast, and before us, off to the southwest, is something that cannot be Kinderhook Creek. This flow is a great, thundering, pounding rush of water. To call this a “creek” is just all out of proportion. It is a sideways waterfall, a foaming, raging, gigantic number six cataract of water. It is a tumultuous cascade, and it is heading towards today’s Chatham Center.
We are the mind’s eye, the human imagination. We can go anywhere and we can do anything. We can fly high and we can fly low and we can fly fast and we can fly slow. Right now we drop down and follow this grotesque caricature of a river. Just above the flow, we can feel a fine spray of water rising above it. When occasional glimpses of sunlight occur, we see rainbows, many of them. But mostly it is a gray sky above. We are nearly deafened by the sound of this torrent. It is an incredible vision.
Is this really the Kinderhook Creek? It seems impossible to imagine it as being that usually lowly flow of water. We are the mind’s eye and we can find out very quickly and very easily. We rise up thousands of feet into the air and look to the north. We find what we expected. There we spy another landmark familiar to those of modern times. Out there is Valatie Creek and it is flowing south toward today’s town of Kinderhook. But even so far away, we can see that it too is another pounding mega-stream. We are drawn towards this vision of Valatie Creek with a strong, almost magnetic fascination. We descend and find our way to the canyon that, in modern times, marks the western edge of the Valatie business district. In modern times, most of that canyon is visible and has only a relatively small stream flowing at its bottom. On the day of our mind’s eye journey this canyon is filled with something akin to an enormous fire hose. Again, it is as if we were looking at a sideways waterfall, compressed by the narrow, rocky canyon walls. The canyon is filled to the brim and, here, the power of the noise is worse than deafening.
Now we are most extraordinarily curious: What has caused all this? Where did all this water come from? What are the explanations of the mysteries we have seen today? We are the mind’s eye; we can, once again, rise up high into the air and that is exactly what we shall do. Soon our mysteries will be solved.
To the north we see a distant mass of whiteness, stretched across the entire northern horizon. We advance towards this new puzzlement; we are perplexed, but we soon see what we need to see. We are approaching a great glacier. It extends off to the west as far as we can see. It also extends an equally far distance to the east. This is the Hudson Valley Glacier. Once again we succumb to a state of overwhelming, compelling curiosity. We are drawn north and closer to the ice. At this time, 14,000 years ago, it is closing in on the end of the Ice Age and, on this day, it is remarkably warm.
The end of an ice age can be a violent time. The glacier is not just melting; it is falling apart. From time to time great masses of ice collapse into heaps of white rubble at the base of the glacier. Huge volumes of water are gushing out of the glacier’s front and flowing on, as a single great torrent, into our prehistoric Valatie Creek. We turn and follow that flow.
Soon, to the west, we spy an enormous expanse of water. We rise up again and it spreads out before us. It is a huge lake; it is a full nine miles to its western shore. In the very far distance we can see the Catskill Mountains rising above that distant side of the lake. This is what future geologists will call Glacial Lake Albany. What an experience! In the distant future geologists will only be able to imagine what the lake looked like, but we are privileged to see it in person. Contact the author at email@example.com
A mind’s eye visit to Glacial Lake Grand Gorge
Robert and Johanna Titus
(First presented on WIOX on Sept. 6, 2016)
We are the mind’s eye, the human imagination. We can do anything; we can go anywhere; we can travel as far as we want, we can travel as fast as we want, as high as we want, and as low as we want.
We can even travel through time.
Right now we are several thousand feet above the town of Middleburgh, and climbing higher. It is exactly 14,000 years ago and below us is the whiteness of a glaciated landscape. This is getting toward the end of the Ice Age. We want to see more.
We ascend to an altitude of a 100 miles and then 500 miles. Now we are looking north. Far in the distance, over the curvature of the Earth, lies Labrador. For millennia it has been snowing heavily up there, and the snow has piled up so thick that it has turned into ice and that ice has become a glacier.
Glaciers, of this sort, spread out from their centers and the front of this one is inching its way south. It has spread across parts of Quebec and it is advancing across all of the Adirondacks. Beyond that, some of it is becoming funneled into the Hudson Valley. Glaciations can be complex events and this one gets worse. A lot of the Hudson Valley glacier peels off and heads west up the Mohawk Valley. And then a lessor amount of that ice advances south into the Schoharie Creek Valley. That is a lot of ice, but it is very small compared to the great ice sheet that covers Labrador.
We are the mind’s eye and we have been following all of this from 500 miles up in the sky. Now we drop down to just a thousand feet above Middleburgh. The glacier we have been looking at can be called a valley glacier. It flows, ever so slowly, within the confines of the steep slopes of the Schoharie Creek. Actually, by glacial standards, it is moving along at a pretty good clip. It has been relatively warm these past few decades and the ice has been melting – a little. Great volumes of meltwater have been trickling and then pouring down fractures within the ice. A substantial pool of water lies at the bottom of this valley glacier. It would normally be moving very slowly in a southerly direction, but now it is actually hydroplaning. There are days when it advances a hundred feet or so. That’s fast!
We, the mind’s eye, drift down the valley. We pass Vroman’s Nose. Its giant ledge of sandstone rises above the ice. We keep going south and more cliffs tower above the glacier, left and right of it. We look down and we see many large curved black fractures in the ice. These are crevasses and they result from the stresses that build up within the ice as is moves. We cannot see this movement, but the crevasses betray it.
We continue to drift south. We are following what will be, many millennia from now, Rte. 30. We pass over what will be the locations of Fultonham and Breakabeen. Have you driven this road? When you return, we want you to stop and get out. Look into the sky and see the ice that was once here. It is something that you really need to appreciate.
Now, we approach the site of Mine Kill State Park and there is a surprise ahead. Suddenly, we pass over the downstream end of the ice. We have reached its terminus. Beyond that are the dark waters of a very sizable lake. Schoharie Creek is one of only a limited number of large rivers that flow north. When a glacier is flowing south, it forms a dam and that is what has happened here. This is Glacial Lake Grand Gorge. It is our main destination today
Map of Lake Grand Gorge. Dark blue is Schoharie Reservoir
We drift very slowly to the south. The waters here are very dark; the lake is 600 feet deep. We turn around and look back at the terminus of the ice. It is a cliff of ice, rising a hundred feet above the waters. The recent warmth of the weather, and all the melting that has been going on, produces fountains of water pouring out of fractures in the ice. Lake Grand Gorge should be filling, higher and higher, with meltwater. We will be watching for this.
The lake is already very large. It is about three miles wide and it runs about ten or more miles to the south, down the Schoharie Creek Valley. Here it is deep and it will only shallow very slowly, upstream, which is to the south.
We turn again and continue our southward journey, soaring through the air. Soon we are acutely aware that beneath us is the site of the modern day world’s Gilboa Dam. We can look down into the waters and envision the dam and the Schoharie Reservoir behind it. You have, no doubt, seen the reservoir; you most likely think of it as a very large body of water. But it is small compared to Lake Grand Gorge. The reservoir is only about a half mile wide and a little more than three miles long. It is only about 150 feet deep; it is just a pale imitation of what Lake Grand Gorge was.
Now we turn east. In that direction lies a great embayment of Lake Grand Gorge. That is where the lake’s waters flooded today’s Manorkill Valley. We drift east over what will be Rte. 990V. We pass Conesville and keep going. Ahead of us is the village of Manor Kill. Have you driven this road? If you do, we want you to look at the valley floor. It is mostly a broad flat landscape. You would be forgiven if you called it a floodplain, but it is not. This is a lake bottom; it is the floor of the Manorkill embayment. Long ago, lake waters rose 150 feet above. Back then, Manorkill Creek, like many others, was flowing into the lake. They were all feeding volumes of water to the lake; the lake should have been rising.
Flat bottom of lake near Manorkill
We turn around and head west, back into the Schoharie Creek Valley. We continue our travel to the south. Soon we pass over what will, in the distant future, be Prattsville. We drift “over the town” and then pass Pratt’s Rock. That ledge of sandstone rises above the lake waters. There were none of Colonel Pratt’s carvings here 14,000 years ago, but the rest of the ledge was much as it is today. Have you climbed to the top of Pratt Rock? If you do, then be sure to look down the valley and see the lake that was once here.
Now we turn to the southeast and follow the lake. In the far distance we spot something white. It is too distant to identify. This is a good time to be the mind’s eye; we rise up a mile into the sky and again look east. In the very far distance we can see the Hudson Valley glacier. Here it is abutting the Wall of Manitou, the Catskill Front. The glacier has filled that valley, right up to its brim and more. Some of its ice has diverted from the mainstream and has been driven up Kaaterskill Clove. A stream of this ice continues into the upper reaches of Schoharie Creek. That is the white we have seen. This is another valley glacier and it is also another dam. The ice has clogged the valley in the vicinity of today’s Hunter. It forms a second, eastern dam, holding back the waters of Lake Grand Gorge. The lake is trapped between two glaciers. We turn around and head back to the west.
We pass Prattsville and see another one of the lake’s embayments. This one extends off to the northwest. Today’s Rte. 23 follows in this path. We drift up this embayment. We can imagine Rte. 23 below us. We reach the site of today’s village of Grand Gorge and see another, lessor, embayment – extending to the west.
This small embayment should be of no particular interest to us, except that we can detect a current of water flowing into it. We look ahead and see that this current is heading toward what is called Grand Gorge – not the village – the gorge itself. Now we are truly drawn – drawn towards this great landscape feature. We appear to be on to something.
We are going in a direction that would take us uphill on Rte. 30 today. But there was no uphill here 14,000 years ago. There was just a flat current of lake water. It was funneling into a narrowing and shallowing canyon. The flow became constricted and it had to speed up. As it speeded up it became increasingly erosive. This is a minor epiphany; we are struck by the fact that we have suddenly stumbled across an explanation for several things that have been bothering us. First of all, this is the current that has eroded Grand Gorge. Have you driven through the gorge? The next time you do we want you to stop and feel the current that was once here. Feel its power. See the canyon it carved.
Grand Gorge – looking north
Then, we have also suddenly learned why the waters of Lake Grand Gorge have not been rising. This is the lake’s “drain.” This is where water escapes from Lake Gorge. We drift to the south and we see the upper reaches of what is today the East Branch of the Delaware River, sometimes called the Pepacton.
Finally, we have learned why the lake is called Lake Grand Gorge.
On this day there is a powerful stream here, a raging, foaming, pounding, thundering torrent of white water. It is eroding a narrow and relatively steep stream valley, just south of Grand Gorge. Have you driven this road? When you do, you will see what the early Pepacton did here.
We continue our journey, heading south to Roxbury. We have left the waters of Lake Grand Gorge and are now following the newborn Pepacton. Roxbury is our final destination; our trek through time is done.