Our reader’s rocks: the origins of flint.

The Catskill Geologists

Robert and Johanna Titus

Dear Bob and Johanna: My husband and I were out exploring north of Rte. 145 (near intersection of County Rtes. 443 and 156) in Berne when we found an interesting outcrop. One of the rock strata had peculiar black masses within it. I am sending a photo. Can you tell me what this is? Debra Teator, Freehold.

Thank you Mrs. Teator. You did the right thing sending us a photo. They can be very helpful. We can’t always identify geologic features from a photo, but this time we can. The gray rock surrounding those black masses belongs to something called the Helderberg Limestone. We expect to be writing a lot about the Helderberg as it is a very important local unit of rock. Its most important aspect is that it takes us back about 400 million years to a time when almost all of our region lay beneath the waters of a shallow tropical sea. If we could transport you to that Helderberg Sea, you would look around and swear that you were in the Bahamas.

The Helderberg Limestone is very well exposed at John Boyd Thacher Park, and we did not know of your outcrop in Berne. The Helderberg is composed of several subunits called formations, and this one is the Kalkberg Formation. Its sediments were deposited well offshore, in waters that were certainly not deep but might be best described as subtidal. If you were at the bottom of the Kalkberg Sea during the daytime, then you could look up and probably see a lot of sunlight.

Now, what is chert and how did it form? Chert is described as being microcrystalline quartz. That makes one of nature’s most common types of minerals: quartz. But, unlike normal quartz, its crystals are extremely small. That’s the easy part; what is harder is figuring out exactly how it formed. Late at night, in geology bars, this has always been the subject of debate. We will tell you our best understanding.

The first thing that happened is that the sediment that makes limestone was deposited. This stuff consisted of very small grains of calcium carbonate (CaCO₃). Most of those grains had previously been parts of the shells of shellfish. Clams, snails and other shell-bearing organisms had died and their skeletons had broken up into grains of sand, silt and clay.

After this sediment had been deposited but before it hardened into rock, it was affected by chemical processes. If we understand it properly, water rich in dissolved silica (SiO₂), was being squeezed out of the soft, wet sediments. When the dissolved silica reached layers of sediment that had a low pH, which is also known as a high acidity, then the microcrystalline quartz crystalized as chert. The chert formed into globs which are commonly called chert nodules. If the nodules grew large enough and were abundant, then they would grow into each other and form strata of chert. That is what is seen in the photo.

So, today’s journey into the past has taken us into 400 million year old sediments and allowed us to watch the formation of chert. This material is better known to most people as flint. That’s the stuff that Stone Age cultures learned to fashion into stone tools, such as arrowheads. It also functioned in flintlock rifles.

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

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An ancient river channel

The Catskill Geologists

The Mountain Eagle Oct. 20, 2017

Robert and Johanna Titus

Every so often, in our columns, we refer to a sizable ledge of sandstone as being the cross section of a Devonian age stream channel. The Devonian part is easy; all of the bedrock in the Catskills is Devonian in age (419 to 359 million years ago). But what about the stream channel part? How, exactly, is it that we know that?

It’s a fair question and we think we should take a crack at answering it. Let’s do that this week. Recently we were over at North Lake, on the Catskill Front. Our primary interests on that day was the ice age history of the land that lies between North and South Lakes. But, we came across a massive ledge of light colored sandstone and it caught our eyes. We took a good look and a good photo. We had seen some interesting structures within the sandstone.

Well, what we had seen were a number of erosion surfaces. We printed up our picture and then inked in those erosions. Take a look at our photo. This had been a sizable river. Its sandstones must be twelve feet or so in thickness. You need a river pretty much that deep just to accumulate all that sand.

This river lay at the bottom of the steep slopes of a mountain range. These were called the Acadian Mountains and they towered above what is now western New England. Streams, that descended their slopes, would have flowed out onto what we call the Catskill Delta. They carried a lot of sediment, most of it sand. These sands came to be deposited where North Lake is today.

These were likely large and powerful streams. They would have been occasionally subject to great flooding events. It is only logical to think that, from time to time, it rained a lot up in the Acadians. Those storms generated powerful flows of water, carrying large amounts of sand. When the streams flowed far enough out onto the delta then their flows slowed down and the sand came to be deposited.

If all that is true, then we should see the evidence in outcroppings, such as the one in our photo. We think that the evidence is there – in the inked lines. Each flood event must have reached a peak, when the flows were at their maximum levels. Those flows, it only seems logical, would have eroded into the sediments of the stream channel. When we inked in those erosional surfaces, we thought we had identified such events. The bottoms of these surfaces are concave and they, each one of them, look like features that had been eroded.

There are at least four of these erosional surfaces in our outcrop, or about one every three feet. We think that each of these surfaces records the peak of a major flood event. During that peak, the flood currents would have picked up large amounts of sand and swept it away. As the flood passed its peak, currents slowed down and most of that sand would have come to rest as a new deposit. Most of the sand in between these erosion surfaces seems to have been deposited at the end of its flood or during quiet times that followed.

How often did these floods occur? We can come up with a very approximate estimate. There are about 4,000 feet of sedimentary rock found in this Devonian sequence and it took about 11 million years to deposit them. That averages out to about 2,700 years per foot of sedimentary rock. If there were three feet per flood and if all the above is true, that means that these floods occurred every 75,000 years or so! That’s a lot of time.

But, most importantly, all this is consistent with the notion that such sandstone ledges were once stream channels.

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

Vroman’s Island

The Catskill Geologists Sept. 2017

Robert and Johanna Titus

We do a lot of poking around, here in the Catskills, and we wind up learning the darndest things about the area’s geology. Let’s do one of those in this week’s column. Let’s start by taking you to Middleburgh. Some time ago we described the fact that the bottom of the Schoharie Creek valley, south of town, is underlain by the silts and clays of an old ice age lake.

About 14,000 years ago, the whole valley here lay beneath the waters of that deep lake. It has been, logically enough, called “Glacial Lake Schoharie.” The flat valley floor, hereabouts, is the bottom of that lake. Most of the time, the waters of a typical lake have a drain which takes them on a journey toward the nearest ocean. Geologists have discovered that the Lake Schoharie drain passed down the Catskill Creek Valley on its way to the Hudson drainage basin. Today Rte.145 follows this path. If you get a chance to drive down this valley, we would like you to imagine the powerful whitewater torrents that once filled up all of its lower parts. Those waters had been in Lake Schoharie, but they had poured into today’s Catskill Creek.

The top of the Catskill Creek Valley lies at an elevation of 1,180 feet at the Village of Franklinton. That level formed a dam for the waters of Lake Schoharie. When Geologists look at the Schoharie Creek Valley, in their mind’s eyes they fill it up to the 1,180 foot level. The floor of the valley lies at an elevation of about 640 feet so, if you do the math. Okay, we will do it; the lake was 540 feet deep! That’s a lot of lake; the next time you are driving south from Middleburgh, look up and imagine all that ice water rising above you.

Well, we had figured all this out and that was when we got to that “darndest” thing. We were looking at our Middleburgh topographic map over, and we noticed that Vroman’s Nose rose to an elevation of about 1,250 feet. Have you ever hiked to the top of the Nose? We hope so, Vroman’s Nose is a hill that is found a short distance southwest of Middleburgh. It looms above the valley floor. It is a very distinctive landscape feature with a towering cliff facing the south. If you have been up there, then you have seen the absolutely wonderful view from that top.

But we had made that darndest discovery. The top of Vroman’s Nose rises about 70 feet above the old lake level. That means .that way back then, this was not Vroman’s Nose; it had been Vroman’s Island.

We hope you will get a chance to visit Vroman’s Nose sometime soon. It’s a town park now and open to the public. You can take one of their trails to the cliff that lies near the top, Today, you can enjoy a wonderful view of the valley spread out in front of you. But we hope you will summon up your mind’s eye, and see the vastness of a very sizable lake out there.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill
geologist.” Read their blog “thecatskillgeologist.com.”

Why Gilboa?

Robert and Johanna Titus

The Catskill Geologists

Sept. 15, 2017

   Gilboa was, a century ago, a sizable town in the center of the Catskills. We have been told it was once as big as Cobleskill. But fate struck; New York City reached out and took the land the town was built on, and used that for a reservoir. A dam was constructed just a little west of the old town. The village was razed and, when the dam was filled with water, it disappeared altogether. What little is left, is at the bottom of the reservoir

It was a sad fate, and one which is still deeply resented. But, why did it happen? What was it about Gilboa that led to its demise? We decided to see if we could answer that question. We could not go back through time and travel to the offices where New York City engineers were making their decisions. We could not talk to them, or read their minds. And, much of the geological evidence is now hidden from sight, at the bottom of the reservoir. But, there are other sources of evidence. Perhaps we could read those minds!

We have one of the maps that those long-ago engineers must have used. It’s what’s called a 15-minute quadrangle map of the Gilboa area, published by the New York State Department of Public Works. Ours is the 1903 edition, so it is the very one that those engineers were likely eyeballing as they searched for likely locations for New York City reservoirs. We could look at this map and think as they must have.

We have selected that part of the map that shows the Schoharie Creek Valley where it stretches from Prattsville, north to the onetime site of Gilboa. That’s where the reservoir went. Take a good careful look. Do you see all those narrow lines? Those are contour lines. They define different elevations. The bottom of the valley was at about 1,050 feet in elevation. If you look carefully, you can see the 1,050 foot contour line, just to the right (east) of the creek.
The bottom of the creek was valley floor flatland. It must have been good farming. Notice the absence of contour lines down there. Flat land has very few, or no contours. But the valley walls are different; there contour lines are closely spaced. A person who, back then, climbed up those slopes would have frequently crossed contours.

Experienced geologists can “read” such maps and learn so much from them. Well, we studied the map and began to see the Gilboa area as it had been, before the reservoir and its dam. We saw that most of the valley floor, all the way south to Prattsville, had been wide and flat. We know that this had been the bottom of something called Glacial Lake Schoharie, and those flatlands must have been lake-bottom silts. Easy to plow, these acres must have been wonderful farmland.

But look where Gilboa was; there the contour lines crowd the valley floor. That’s where the Schoharie Valley had been surprisingly narrow. Those long ago engineers must have seen the potential. Gilboa was located right where the valley was narrow and easily dammed. Behind that planned dam, was a wide valley with a flat floor.

The Gilboa site was ideal for damming; the lands behind that dam would be perfect for a reservoir. Gilboa’s fate was sealed; the town was doomed; the town was damned!

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

A visit to Glacial Lake Windham

The Catskill Geologists

Robert and Johanna Titus

The Mountain Eagle – Sept. 8, 2017

Last week we visited Windham, actually the Windham Path, just east of town. We wanted to show you something about the ice age origins of the town. Most of the Windham Path lies upon the floor of what’s called a glacial lake. That lake had come into being when a glacier deposited heaps of sediment in something called a moraine. The moraine can be seen just east of the Path. Most of the land from east Windham to here is rolling elevated moraine landscape. That’s the land lying just east of Mitchell Hollow Road.

Let’s learn some more this week. We would like you to drive west from Windham on Rte. 23. You may have done this before, perhaps many times. But, as always, we want you to be paying more attention to the landscape that you are passing. We, especially, want you to take heed of the flat landscapes down at the bottom of the valley. It would be easy to dismiss this as a floodplain, after all valley floors are supposed to display floodplains. But, you would be wrong; this flat landscape is the floor of an ice age lake. Lake deposits are almost always spread out as flat sheets. That’s what we see here.

These lake bottom landscapes continue at least as far west as Ashland. They speak to us of a glacial lake. It was a big one, extending at least five miles from the Windham moraine to a bit west of Ashland. Rte. 23 lies on a platform that runs parallel to the old lake. That platform also has an ice age origin. It is composed of sediments that were dropped down the northern valley wall and deposited as a lakeshore deposit called a glacial terrace. That terrace was irresistible to highway engineers when they were making Rte. 23. It lifted the highway up onto a well-drained surface.

The top of the terraces was deposited at just about the old lake level. Our topographic map tells us that that level was at about 1,500 feet in elevation. The map also tells us that the lake bottom lay at about 1,450 feet. We can thus calculate that the lake was about 50 feet deep. It got a good bit deeper toward Ashland. Turn south (left) at Jewett Heights Road and, when you get down to the river, stop and get out. You are now standing on the floor of a deep lake! Have you ever done that before?

You might do a little exploring. Look for a vantage point, somewhere above the 1,500 foot level. Now you can look down and, in your mind’s eye, you can survey Glacial Lake Windham as it once was. We picked a day, very late in the Ice Age. The climate had been warming up considerably and the ice had melted off most of the lake’s surface. There was, however, still a narrow shelf of gray ice all around the lake’s shore.

We were hoping to see some animals. Perhaps a mastodon or two might have been walking the shores of the lake. But, we were disappointed. It was not that late in the Ice Age, it was still too cold in Windham.

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

The Ice Age at Windham – Part one, an introduction

The Catskill Geologists; The Mountain Eagle; Sept. 1, 2017

Robert and Johanna Titus

We understand that we have a number of new readers in the town of Windham, and we are glad about that (Sept. 2017). Let’s begin today a series of articles about the ice age history of that town. We can start at the relatively new Windham Path, located in the Batavia Kill Valley about a half mile east of town. It was opened about four years ago and offers some pleasant and easy walking.

Take a look at our photo. Most people see an inviting place for recreation; naturally we see geological history. Our photo was taken from the path’s parking lot. If you go there we would like you to look straight ahead into the distance. Notice the broad flat surface on the distant right of our photo. Now take a look to the left. Our picture shows a low tree-covered hillock spread out east of those flats.

Most people just see landscape; let’s learn what the two of us see. That hillock on the left is what geologists call a moraine. That’s a heap of earth that was brought to where you find it by an advancing glacier. We look at it and, in our mind’s eyes, we see a glacier advancing from the right. It was advancing because the climate had been getting colder – cold is good for glaciers, right? But by the time our glacier reached the left side of this view, climate change had begun; it started warming up and the glacier began melting away – retreating to the right.

During its advance, that glacier had been bulldozing large amounts of earth, all of it piled up at the front of the ice. But, when the glacier was melting away, all that earth came to be left behind. That’s a moraine; this heap of earth speaks to the two of us of an important chapter in the ice age history of Windham.

What happened next? The retreating glacier was backing down the Batavia Kill Valley. It acted as a dam and that formed a glacial lake, lying between the retreating ice and the moraine. It’s the sediments of that lake that make up that flat lying surface in the distant right.

You might go there and do what we do. We always keep a barbeque skewer in the back of the car. We bring it down to flat surfaces like this one, and try to drive it into the ground. If, as we expect, we have found a lake deposit then the skewer will easily slide into the ground. If it doesn’t, it has hit a rock and it is not a lake deposit. Lake sediments are all silt and clay and don’t have rocks in them.

Well, we have seen the Windham Path as most people don’t. We gaze at it and we see an ice age landscape; we form visions of what it was like here at the close of the Ice Age. It can be an exhilarating experience.

But it is important to take this information and use it to form a broader picture of ice age history in the Batavia Kill Valley. Let’s get back in our car and head west on Rte. 23. We notice, right away, that we are crossing an elevated landscape with rolling and sinuous hillocks. This landscape continues until just past Mitchell Hollow road at the eastern end of the Windham business district. We have found another moraine and this one is a bigger one. Like the one at the Windham Path it speaks to us of a glacier advancing east through the Batavia Kill of long ago.

We have learned a lot about Windham, but we have a lot more ahead of us.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist” and read their blog at thecatskillgeologist.com.

The Ice Age at Windham – Part one, an introduction

The Catskill Geologists; The Mountain Eagle; Sep. 8, 2017

Robert and Johanna Titus

We understand that we have a number of new readers in the town of Windham and we are glad about that. Let’s begin today a series of articles about the ice age history of that town. We can start at the relatively new Windham Path, located in the Batavia Kill Valley about a half mile east of town. It was opened about four years ago and offers some pleasant and easy walking.

Take a look at our photo. Most people see an inviting place for recreation; naturally we see geological history. Our photo was taken from the path’s parking lot. If you go there we would like you to look straight ahead into the distance. Notice the broad flat surface on the distant right of our photo. Now take a look to the left. Our picture shows a low tree-covered hillock spread out east of those flats.

Most people just see landscape; let’s learn what the two of us see. That hillock on the left is what geologists call a moraine. That’s a heap of earth that was brought to where you find it by an advancing glacier. We look at it and, in our mind’s eyes, we see a glacier advancing from the right. It is advancing because the climate had been getting colder – cold is good for glaciers, right? But by the time our glacier reached the left side of this view, climate change had begun; it started warming up and the glacier began melting away – retreating to the left.

During its advance, that glacier had been bulldozing large amounts of earth, all of it piled up at the front of the ice. But, when the glacier was melting away, all that earth came to be left behind. That’s a moraine; this heap of earth speaks to the two of us of an important chapter in the ice age history of Windham.

What happened next? The retreating glacier was backing down the Batavia Kill Valley. It acted as a dam and that formed a glacial lake, lying between the retreating ice and the moraine. It’s the sediments of that lake that make up that flat lying surface in the distant right.

You might go there and do what we do. We always keep a barbeque skewer in the back of the car. We bring it down to flat surfaces like this one, and try to drive it into the ground. If, as we expect, we have found a lake deposit then the skewer will easily slide into the ground. If it doesn’t, it has hit a rock and it is not a lake deposit. Lake sediments are all silt and clay and don’t have rocks in them.

Well, we have seen the Windham Path as most people don’t. We gaze at it and we see an ice age landscape; we form visions of what it was like here at the close of the Ice Age. It can be an exhilarating experience.

But it is important to take this information and use it to form a broader picture of ice age history in the Batavia Kill Valley. Let’s get back in our car and head west on Rte. 23. We notice, right away, that we are crossing an elevated landscape with rolling and sinuous hillocks. This landscape continues until just past Mitchell Hollow road at the eastern end of the Windham business district. We have found another moraine and this one is a bigger one. Like the one at the Windham Path it speaks to us of a glacier advancing east through the Batavia Kill of long ago.

We have learned a lot about Windham, but we have a lot more ahead of us.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist” and read their blog at thecatskillgeologist.com.

The New Kaaterskill Falls Overlook

The Catskill Geologists, The Mountain Eagle, Aug. 17, 2017

Robert and Johanna Titus

Have you been to Kaaterskill Falls lately? People have been visiting there for two centuries. We have seen initials carved into the rock there dating back to 1810. It was probably landscape artist Thomas Cole who first made it famous with his paintings, done in the 1820’s. It’s scenic but, it is a dangerous place; many people have died there.

Something needed to be done. Work began in recent years. The whole trail system, approaching the falls from downstream, has been refitted. But our focus today is on the new trail to the upper falls. You get there by taking Rte. 23A east to Haines Falls. Then you turn left onto County Route 18 and continue east. Turn right onto Laurel House Road and drive to the end. If you have been there in the past you will be pleasantly surprised by the new parking lot. You will have no trouble finding the new trail. It’s right there. It is paved and winds back and forth through the woods in a fashion that allows it to have nothing more than a gentle slope, making it all the more accessible for the elderly and probably even for those on modern powered wheel chairs.

When you get to the end of the trail you will find a fine viewing platform with sturdy guard rails. The bars are high enough to provide safety and thin enough so that they do not block the view. And what a view it is. They were careful to select just the right spot for this platform.  You look down and see all of the upper falls. Our photo could not do justice to this view; you will just have to go there yourself. You can scan sideways and see, off in the distance, High Peak and Roundtop Mountains. It is a much better view than could ever have been seen in the past.

And we are sure that it will be a lot safer than the old trail, the one that went to the top of the falls. Nobody is likely to want to climb over the bars here, so it is far less probable that there will be so many accidental deaths. If you insist, you can find the old trail and you can go and visit the top of the falls, as in the past. But they have made that trail unobtrusive and we are guessing that there will be much less traffic in that direction. That will only allow limited numbers of people going where the dangers are greatest.

   There must be some good geology here or we would never have paid much attention to the place. There is. Take a good look at our photo. There are three massive ledges of Catskill sandstone, commonly called bluestone. One is at the top, or the lip of the falls, and the second is halfway down and hard to see. The third makes up the platform at the bottom of this, the upper falls. All this belongs to a unit of rock called the Oneonta Formation, a late Devonian aged rock formation that can be traced all across the upper Catskills. It is part of the fabled Catskill Delta. Those sandstones are ancient river deposits. Those ledges were once sands, and that sand filled the channels of rivers that crossed the old Catskill Delta.

In between those sandstones are thicknesses of brick red shales. These comprise more of the Catskill Delta. They formed, originally as overbank deposits. That is, they formed as floodplain deposits in between the old river channels. So, altogether, the strata of Kaaterskill Falls constitute a very representative cross section of the Catskill Delta.

Make sure you go there soon. We applaud what has been done at Kaaterskill Falls. Two thumbs up!

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

Time lines

The Catskill Geologists

Robert and Johanna Titus

The Mountain Eagle 2017

Late at night in geology bars, we geologists ponder deep thoughts about what geologists call “deep time.” We would like to relate some of those thoughts to you in this week’s column. It’s an account of what we visualize when we drive south a few miles from Middleburgh on Rte. 30.

Any time of the year this is a scenic drive. Left and right, we pass beautiful agricultural fields. This is a remarkably flat landscape and much of it is fertile land; it has been farmed for centuries and all farmland is pretty. Then there are several scenic hamlets, including Fultonham and Breakabeen. We like to sometimes stop at the farmer’s markets along the way. This is the modern world that we are traveling through, and Rte. 30 provides a very nice view of it. When autumn is coming up; you should take this drive.

But, we are geologists, and we are always finding ourselves in the distant past. Did you read our recent column about this area? Then you know some of what we see when we do this drive. We related how this stretch of the Schoharie Creek Valley was once the bottom of an ice age lake. That was, perhaps 14,000 years ago when the ice age climate was warming up and the glaciers were melting away. We learned that this lake was hundreds of feet deep back then. If Rte. 30 had passed across that lake bottom then it would have been a pitch black road.

The next time you are there, stop and take a look around. We like to say that we are able to “savor” time at places like this. This broad flat valley floor has two manifestations in time. It is the world we see and that same flat surface was also the bottom of a substantial lake. This flat landscape has led at least two lives. You can imagine the thoughts this generates in a geology bar.

But, there is actually a lot more. When you explore the area, here and there you will encounter stratified bedrock. These exposures are mostly sandstones and shales, and it is not unusual for them to be rich in the fossils of marine shellfish. There are some substantial outcrops. One is at Vroman’s Nose. The next time you climb that “nose” watch for outcrops of stratified rock along the way. Drive south again and watch for more exposures along the way. It’s the same thing; those strata are frequently rich in fossils.  Each stratum was formed on the bottom of a sea. It gets better; each stratum was the bottom of a sea.

Perhaps you are getting the drift of today’s column; we have been describing a single flat surface that extends south from Middleburgh. It is a surface that exists today and, in this form, it is a very scenic location. But there is so much more. This surface has existed several times in the distant past. It was, 14,000 years ago, the bottom of an ice age lake. It was just as flat then but under hundreds of feet of glacial meltwater.

Then there was that third time our surface existed. About 380 million years ago it was the bottom of a saltwater sea. Geologists call landscapes like this “exhumed.” As such they are landscapes that reveal episodes of time from the very distant.

We hope you will enjoy this ride in the country during the coming leaf season. Pull over, get out of your car and “savor” our geological history.

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

A Fossil River Runs Through Woodstock

On The Rocks, The Woodstock Times

Updated by Robert and Johanna Titus

There is one very good thing about geology – you don’t have to travel very far to go see it. That’s certainly the case here in Woodstock. As we drove into town of Woodstock one day we stopped and took a long look at the rock outcropping at the intersection of Rt. 212 and Chestnut Hill Road. That’s just east of town. The rocks there belong to a unit called the Kiskatom Sandstone. They were deposited long ago as sediments on the outer edge of the great Catskill delta complex. Once again, the rocks took us back to a Devonian age Woodstock, maybe 380 million years ago.

We knew the images that these rocks would generate in our imaginations. We could look east and, in our mind’s eye, we could see the towering profile of the old Acadian Mountains rising on that horizon. The Catskill delta lay below the mountains. It was an enormous expanse of fast-flowing and sluggish streams, with swamps, bayous, lakes and ponds. Here and there, we could see dense but primitive foliage’s of primitive plants. This was the setting in which the rocks of Woodstock had first accumulated as sediments.

All this was vague imagination, but an outcrop is made up of real rocks and real rocks usually have very specific and often very interesting stories to tell. Here, at the Chestnut Hill intersection, there were two types of lithologies and two stories. The most striking rocks were the massive sandstones that made up the upper half of the exposure. Sandstones are just what they sound like, masses of cemented sand. These sands were deposited in strata which were inclined, first one way and then another. The sets of strata intersect each other in a pattern called “cross bedding.” From plenty of experience we knew what this meant. We were looking at sediments that had been deposited in one of those old delta rivers. The cross bedding formed as the sands were buffeted back and forth by changing currents associated with the rising and falling of the river’s flow. Each set of strata recorded an everyday moment in the history of that nameless old stream.

The finer grain deposits below the sandstones were different. They were more thinly laminated and composed mostly of silt and clay, now hardened into shale. Its color caught our attention, the shales were reddish. That’s a common color for rocks throughout the Catskills. This soft, brick-red is an indicator of terrestrial conditions, the shales had not been deposited in a river, but they had been the soils that formed on the banks and in between the streams.

When you go there, you will notice that there is a sharp boundary between the channel sandstones and the red soils. That’s not unusual, after all, rivers get to where they are by eroding through the surrounding countryside. This old river had cut its way through the Devonian flood plain soils.

There are ironies in the study of ancient rocks. We were acutely aware that the old river occupied the very space where the Saw Kill is today. Woodstock, then and now, was flood plain. There’s no relationship between the two rivers. They each occupied the same space, but they existed nearly 400 million years apart in time. Because of its age the old river may seem like an abstraction, or somehow less real than today’s Saw Kill. It’s not, in its time it was just as real as the Saw Kill is today. And 400 million years from now, both of them will be equally lost in time. That’s just the way it is. We, all of us, play out our roles on this planet and then disappear into time.

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