Robert Titus - page 44

                               The Hyde Park Deltas – Part two

thecatskillgeologist.com

Robert and Johanna Titus

Nov. 2016

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This is the second of two new articles about the Hyde Park deltas.

Last time, we began investigating the Hyde Park Deltas. These ice age features have been recognized by glacial geologists for decades and they are seen on the New York State Museum’s map of New York State glacial geology. That map recognizes two deltas.  But we have found something remarkable and, we feel, revealing. Those two deltas represent two chapters of delta formation. That needs to be explained. So – we are going to, herein, record the sequence of events that we have deduced to, we hope, explain all this. We are, in short, going to record a sequential history of the formation of the Hyde Park Deltas – and thus Hyde Park itself.

1) It all began sometime close to the end of the Ice Age. The Hudson Valley glacier had been melting and vacating the valley, and it left behind a sizable lake. That has long been recognized as Glacial Lake Albany. The lake stretched across the Hudson Valley and, at Hyde Park, it was nearly two miles wide.

   2) Crum Elbow Creek was flowing south by southwest, east of, and parallel to, the lake. This took it across a newly deglaciated landscape. We suspect that, at least at first, it was a far more powerful stream than it is today. It does not amount to much today, but back then, it may have been swollen with very dirty meltwater. It, we think, it (must) have been a very erosive stream.

Crum Elbow Creek today, upstream.

3)  If so, then Crum Elbow Creek had to have carried a very substantial load of sediment which came to be deposited in Lake Albany. Most of that sediment formed what we are calling the Roosevelt Delta (see yellow on our map). The waters of Lake Albany, at that time, reached a level of 180 feet in modern elevation. The delta’s topset was, likewise, at today’s 180 feet.

The Hyde Park deltas; Roosevelt Delta in yellow; Vanderbilt Delta in brown.

4) We conclude that, back then, Crum Elbow Creek did not turn sharply to the west as it does today. Instead, it continued its southwest path which took it past today’s Wallace Center and onward, just a little north of the Roosevelt mansion, Springwood. Its old channel can still be seen adjacent to the parking lot at the Wallace Center (see map and see photo). This is the time when the stream deposited the Roosevelt Delta (again, see our map).

“Old” Crum Elbow Creek, highlighted in red. “New” Crum Elbow Creek (blue) extends off to the west.

Now dry channel of “Old” Crum Elbow Creek, just north of Wallace Center. “Old” Crum Elbow Creek once flowed at the bottom of this small valley.

   5) Next, there came a time when Lake Albany (suddenly?) drained down to a level of 170 feet. We do not know why, but with that lowering, a remarkable event ensued. A small stream, one that had just begun flowing along the northern edge of the Roosevelt Delta, became quite erosive and, by headward erosion, it worked its way up along that northern flank of the Roosevelt Delta. Stream piracy was now occurring. The path of this stream, “New” Crum Elbow Creek, can be followed along East Market Street (aka County Route 41). It can be seen that this stream had been erosive enough to cut down into the bedrock there (see our photo) and create something of a canyon.

East Market Road follows canyon of “New” Crum Elbow Creek. The creek is just out of sight on the far right; it presumably cut the steep slopes of this canyon.

6) With time, this growing creek would intersect “Old” Crum Elbow Creek and divert its waters into the present-day path of “New” Crum Elbow Creek.  Also, a new delta, our “Vanderbilt” Delta, began to form. This younger episode of delta building apparently did not last as long as the previous one, and the new delta never got to be as large as its predecessor. The old Roosevelt Delta leveled off at 180 feet; the new Vanderbilt one at 170.

7) During the period of stream piracy, “Old” Crum Elbow Creek continued flowing in its old path. But that path was about ten feet higher above the new level of Lake Albany. This higher level promoted active erosion of the “Old” Crum Elbow channel. This old channel is the one visible just north of the Wallace Center parking lot. More of the old channel can be traced through Hyde Park.

More channel of “Old” Crum Elbow Creek (left center) on the Yellow Trail at the Winnakee Nature Preserve, just north of Rte. 9.

8) After stream Piracy was complete, the “Old” Crum Elbow channel was left high and dry as is seen at the Wallace Center today (our photo, above). Another dry channel can be seen immediately north of the old Roosevelt family stables. (See our photo below). That had been a tributary of Old Crum Elbow Creek.

Dry canyon of a tributary of Old Crum Elbow Creek, just north of Roosevelt family stables on the Cove Trail.

Sometime later, Lake Albany dropped the remaining 170 feet, down to its present level. Today’s “New” Crum Elbow Creek came into its modern form by eroding those 170 feet. This is best seen where the bridge crosses the creek at the south end of the Vanderbilt Estate.

Crum Elbow Creek at the Vanderbilt Estate.

We believe that this history accounts for pretty much all the landscapes we see, today, at Hyde Park. It is an account that describes the very origins of Hyde Park itself and is thus a fascinating history. We invite you to tour the town and see the geologic sites that we describe here. Then, take Rte. 9, north and south of Hyde Park, and see what the vicinity would have looked like if the deltas had never formed.

We have long been impressed with how ice age events explain so much of what we see in our scenic Hudson Valley. This is a fine example.

            The Hyde Park Deltas – Part one              

   Thecatskillgeologist.com

Robert and Johanna Titus

   Nov. 2016

Most of the time we are re-running old newspaper columns on this site. But we expect to do some original work as well. That is the case here today. We are publishing the first half of a study we recently did on the geology of the Hyde Park ice age deltas. We hope that you will be able to go to Hyde Park and see what we have seen. We are publishing this again because we have new photos for Part Two

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The town of Hyde Park is built upon a broad flat platform. It’s a natural landscape feature and it needs to be understood. When you drive into the town, we want you to take note of it. From the north, you pass the Vanderbilt Estate with its endless front lawn. Then the highway passes through the urbanized part of the town. That area is just as flat. Farther south is the Roosevelt Library and Museum. See its expansive and, again, very flat grounds. All this flatness begs to be understood. There is a pattern here, and we always say “when Nature presents scientists with a pattern, she demands an explanation.”

We like to bring a barbeque skewer along with us wherever we go. When we want to investigate this sort of flatland we try to drive it into the ground. If there are rocks, which there usually are, we have little luck. But – if the skewer slides in easily – then we have likely found a glacial lake bottom. That is the case at Hyde Park. Take a look at our map. All the yellow is flatland where there are few, if any, rocks in the ground.

Yellow on map is delta flatland. Base map courtesy of US Geological Survey

But, is this a simple lake bottom or is there more to the story? Notice that, on our map, the yellow flatlands lie at the downstream end of a stream with the unlikely name of Crum Elbow Creek. Long ago, glacial geologists recognized that that all these flatlands comprised an ice age delta, sometimes called the Hyde Park Delta, the delta of Crum Elbow Creek. The New York State Museum map of ice age features actually portrays two deltas here, one north of Crum Elbow Creek, with a second and larger one, just to the south. This is important, and we should name the two deltas. Let’s call the northern one the Vanderbilt Delta (brown) and call the other the Roosevelt Delta (yellow).

Roosevelt Delta in yellow; Vanderbilt Delta in brown.

Back during the Ice Age, there was a sizable lake flooding all of this part of the Hudson Valley. It has been called Glacial Lake Albany. Crum Elbow Creek is a long flow of water and, back then it was likely carrying a lot of sediment. Most of that sediment was deposited as the delta where the creek flowed into Lake Albany. The top of a delta is always flat and it roughly corresponds with the old lake level. That’s called the topset of the delta. That would have been at about 180 feet in today’s elevation.

The front of a delta is typically a steep slope called a foreset. That explains another landscape feature that we see throughout Hyde Park. Take a look at our photo from the Vanderbilt mansion. The mansion was located at the top of the steep foreset slope. That offered the Vanderbilt’s a nice view of the Hudson River. Walk north and south from the mansion and enjoy this view.

The Vanderbilt Mansion from the south. Below it is the foreset slope.

Foreset slope, north of the Vanderbilt mansion, with its view of Hudson.

Now we have learned a lot about Hyde Park. You are not likely to be able to pass through town without envisioning yourself in a very different landscape, an ice age one. With your mind’s eye look west and see Glacial Lake Albany spread out before you. It extends all across the Hudson Valley. The lake was almost two miles wide here. That’s about four times as wide as today’s river is.

But, the more we worked the area, the more we saw problems that needed to be explained. For starters, we thought the flow of Crum Elbow Creek was a bit odd. The stream has its head about ten miles north of Hyde Park. It flows in a remarkably straight line, just a little west of south, all the way to Hyde Park. Much of the way, it follows Rte. 9G. But then, at the village of East Park, it turns sharply to the west and flows directly into Hyde Park and, from there, into the river (see our maps).  Back during the Ice Age, that took it right into Glacial Lake Albany. We wondered if there was a story to that sharp westward turn. We are scientists; again, we are supposed to wonder such things.

Then it began to bother us that Crum Elbow Creek did not match the delta all that well. It certainly did a good job of explaining the northern part of the delta, the Vanderbilt Delta. But how was it that the delta spread out so far to the south? How could delta sediments extend a full two miles, south of Crum Elbow Creek? In short we just did not think that Crum Elbow Creek was accounting for the Roosevelt part of the delta complex. Again, we are scientists.

That’s when another problem appeared. We were now looking more carefully at the map and we suddenly noticed that, while there were two deltas at Hyde Park, they were also of two different elevations. The Roosevelt Delta, south of Crum Elbow Creek, had a topset at about 180 feet in elevation, but the Vanderbilt Delta, north of the creek, lay at just about 170 feet. We were, clearly, looking at two separate events.

This is when it started getting exciting. We soon had a flash; all of a sudden we saw what had happened, and that was a genuine epiphany. We will be back next Thursday with the solutions to these problems, but in the meantime we want you to have a chance to ponder them, and see if you can come up with the solution yourself. We leave you with a blown-up version of our map, focusing on the southern part of the Roosevelt Delta. Take a good look and see if you can solve these problems without our help.

Do you have some ideas? Write to our facebook page “the Catskill Geologist.”

Close-up of the southern delta.

THE BLUES ON A RAINY NIGHT

On the Rocks

Robert Titus

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

Robert Titus

July 2^nd, 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 19^th 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 titusr@hartwick.edu

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.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.”

A Petrified Delta

Windows Through Time

Robert Titus

June 26^th 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!

Contact the author at titusr@hartwick.edu

Fractures from the distant past.

Windows Through Time

Robert Titus

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 titusr@hartwick.edu

The Wall of Manitou

Windows Through Time

Robert Titus

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 19^th 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.

Reach the author at titusr@hartwick.edu

Flocks of geologists

Windows Through Time

Robert Titus

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 titusr@hartwick.edu