Robert Titus - page 4

Floodplains? Part One

The Catskill Geologists

Robert and Johanna Titus

We are guessing that you have a pretty good idea of what a floodplain is. That’s the flat surface which stretches from one side of the valley to the other. Right? Well, maybe, and then maybe not. These next two weeks we are going to visit a pair of “floodplains” and find out something very different. Let’s begin.

Our first so-called floodplain lies in the valley of the Batavia Kill, next to Rte. 23, just a little west of the town of Windham. Take a look at our photo taken along the highway. You see the very emblem of a floodplain, or so it would seem. This flat surface stretches down the valley almost to Prattsville. And, it is just as flat all the way. If you get a chance, take this drive and see what you think.

So, why is this not a floodplain? We weren’t fooled for even a minute. When we got a chance, we climbed down off the road with a barbeque skewer. That’s a bit of equipment we always carry in the back of the car. We use it when we see valley floors that look like this. We take the skewer out onto the supposed floodplain and drive it into the ground. If it goes in smoothly and all way, we try again, and then even one more time. With repeated successes we become confident that there are no cobbles or even bits of gravel in the ground. The eliminates the floodplain hypothesis. You see, the typical floodplain is composed of sediments carried along by a stream and then deposited during flood events. Fast flowing streams have no trouble carrying gravel and cobbles. Flood events have no trouble depositing them and making a new floodplain composed of course-grained sediment.

But what happened is that the barbeque skewers slid into the ground smoothly. There are no cobbles and no gravel to get in the way. What is there is a combination of sands and silts. Those are the deposits of lakes. Batavia Kill is a long and old lake bottom.  We find this all the time and all through the Catskills and Hudson Valley. That’s because there are likely to be lake deposits in all these vicinities. How come?

The answer is that these are glacial lakes that date back to the Ice Age. And, again, how come? We kept driving west along Rte. 23 and we approached the vicinity of Red Falls. Have you seen Red Falls? It’s a pretty cataract composed largely of red sandstones, lying a bit east of Prattsville. It’s worth the trip come warmer weather. Just east of those falls the valley is altogether different. There is nothing that even resembles a floodplain. Instead, great heaps of earth crowd the streambanks. This landscape is called a glacial moraine. That is something with its own story.

We have, once again, gone back to the Ice Age. We look east and we see that the Batavia Kill Valley is filled with ice. One glacier advances from the east while another approaches from the west. On the day that we make our time-travel visit, they are colliding. An enormous pile of earth lies compressed between the two. It’s a heap of earth called a glacial moraine. Our time travel continues, and we watch as the climate warms and the ice begins to melt. Soon a lot of it melts back and the glacier retreats toward Windham. Now that Red Falls moraine is left behind as an earthen dam. And behind that dam lies a growing lake. Let’s call it Glacial Lake Batavia.

Over time, the lake will accumulate a lot of sediment. When it drains that sediment will be left behind as a flat surface, that looks like a floodplain – but isn’t.  Let’s do something like this again next week.

Take this drive sometime soon and see how your understanding of the valley has changed.

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

Christmas rocks? in January?

The Catskill Geologists

Robert and Johanna Titus

Jan. 25, 2019

Have you joined our facebook page yet? We have been running it for several years now. It’s called, logically enough, “The Catskill Geologist.” We post notices of all our newest articles in it. Also, when Robert has a working memory, we post schedules of our upcoming speaking events, hikes and whatever else is keeping us busy. The page gives you a chance to be more engaged with what all we are up to. We have nearly three thousand members, so we hope you will join too. Soon.

All our members are able to actively participate in our facebook page and many do. We have had any number of people post pictures of geological phenomena that they have found. Often, they really do not know what it is that they are posting, but we can typically identify it or find someone who can. If all this sounds like something you would enjoy, then do join us.

Recently a member sent in a photo of a rock that he found in the upper Esopus Creek Valley. It was one of those catches-our-attention kinds of rocks. Take a look at his photo. You will quickly see what interested him. It’s a Christmas sort of rock, isn’t it? See the bright red color mixed with the green. Well, we recognized it right away. This sort of rock is referred to as being “mottled.” That’s a rock that displays a mixture of colors. They aren’t always reds and greens, but this one is so let’s talk about it.

But, first things first. We always like to say that the hardest thing to see in science is something that is not there. That’s the case here. This rock came from the Catskills, so it should be a stratified sedimentary rock; that is, it should be layered. But it is not stratified and that will turn out to be important.

The colors are the most important things. The red is typical of soils that form in tropical or subtropical settings. Have you ever heard of Georgia red clays? They are red soils found in Georgia. They formed during the last big interglacial time when the climate down there was a lot warmer and more humid than it is today. This sort of soil can be thus be called a tropical soil. Such soils today, commonly form within rain forests. There is always a lot of iron in any soil and the red color means that it is oxidized; it combined with oxygen. That occurs most often in the upper soil horizons where a good amount of air (with oxygen) is likely to be found.

So, what does the green mean? Green colors in this sort of soil occur farther down where it is likely to have been soaked in groundwater. That’s below the water table. Here there is much less oxygen for the iron to combine with and we say that the soil in not oxidized but reduced. Well our facebook member has found a rock that formed near the top of the water table where both oxidized and reduced soils can be found.

In either event we are looking at a soil forming processes, so this is a petrified soil, although not an especially good one. Soils are not typically stratified so that is consistent with what we have seen. It takes us back to the middle Devonian time period, about 380 million years ago, when the Catskills were not mountains, but a great tropical delta with red soils forming on it.

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

Bluestone sidewalks

The Catskill geologists; Jan. 2019

Robert and Johanna Titus

Do you remember the words from Joanie Mitchell’s old song “Big Yellow Taxi?” “You don’t know what you’ve got ‘til it’s gone.” We certainly learned that when Hurricane Irene destroyed the old covered bridge at Blenheim. It was one of the last few such bridges in our region. Once there were many of them, but now they are all nearly gone. Long ago, people would have just taken each of them for granted. Then they were, one after another, taken down and replaced by far more modern bridges. That was chalked up to “progress.” Then they were nearly gone, and we came to know what we had, but only after it was nearly gone.

How many times have you seen “We buy old barns” signs along the highways? Old barns can be torn down and their wood commands a premium price. Do you take much notice when you pass an old barn? Perhaps you won’t notice any of them until they are nearly gone. We fear that may well happen. It’s a sad thought.

Why are we talking about these things in what is supposed to be a geology column? Well, for a very good reason. Our region was once densely dotted with bluestone sidewalks. There had been a very large bluestone industry throughout the Catskills and much of that industry was devoted to making stone slabs for those sidewalks.

We have written about bluestone a number of times in this column. It’s a form of sandstone that was deposited in river channels that crisscrossed the Devonian aged Catskill Delta that once covered the Catskills region. That was back about 375 million years ago. Bluestone made a very good sidewalk material; it was tough stuff and held up very well under long periods of heavy use. It did not get slippery when wet, so people didn’t much have to worry about falling. And it was good looking, adding to our region’s rustic beauty. But then bluestone sidewalks began to disappear. And then a lot of them followed.

Good quality cements came along, and they could be turned onto fine sidewalk slabs. When an old bluestone sidewalk wore out, it was only sensible to replace it with cement. Progress had struck again. These modern cement sidewalks work just fine, and they are less expensive. But they just aren’t the same. Walk a cement sidewalk and see if you can feel the absence that the two of us feel. There is little beauty in cement, there is none of bluestone’s rusticity and nothing that can be called heritage. There is just a palpable absence in cement. And the more you think about it, the more you notice it.

Don’t get us wrong; we are realists. We know the era of bluestone is over. It will not likely return. Our efforts here are simply to call your attention to these old sidewalks. You cannot likely pass a covered bridge without noticing it, but it is easy to miss a bluestone sidewalk. We would like it if you looked around and watched for bluestone in your neck of the woods. We are fortunate to have a good one in our hometown of Freehold. See our photo. Perhaps you can find one near your home. We hope so; let us know if you do.

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

A fossil tree on an ancient trail

The Catskills Geologists; The Mountain Eagle

Robert and Johanna Titus

Dec. 13, 2018

We get a lot of email from our readers and sometimes they send us good leads on potential columns. That happened recently when a reader sent us a photo of a fossil that he found along the trail that leads up to Kaaterskill Falls. Have you been on that trail? It’s been there forever but has been nicely renovated in recent years. It makes a scenic hike. It’s not a difficult one and you are rewarded with a view of Kaaterskill Falls from below. That’s the view that Thomas Cole made famous with one of his first truly successful paintings done in the 1820’s. That view was important in the history of American art itself. If you haven’t been there, then you should.

We have hiked the trail many times and never tire of it. We haven’t had a whole lot of success in finding fossils along it, but they are there. If you have a sharp eye and if your eye is a trained one, then you do find the occasional fossil plant. These are trees from the famed Gilboa Forest. Those are New York Sate’s most important fossils; they make up the world’s oldest known forest ecology, dating back about 380 million years.

We know! We know! December is not a very good time of the year to go fossil hunting, but when the weather warms up, you might give it a try. We, ourselves, have found some fairly decent fossil tree trunks in the massive sandstones of Bastion Falls. That’s right above the highway at the hairpin turn on Rte. 23A. Maybe you can do us one better.

Our reader did just that. He found the branch of a fossil tree, complete with a row of leaves. Take a look at his photo. We immediately recognized the specimen. We had

already seen a very similar specimen in Bearsville. One of our Woodstock Times readers had found it in a quarry above her home. Take a look at our second photo for that one which is a much better–preserved fossil. See how much better the leaves look. We thought that both specimens belonged to a tree named Archaeopteris, but we wanted to be sure. So, we sent both photos off to friend Dr. Charles Ver Straeten at the New York State Museum. Chuck sent them on to two of the most foremost experts on Gilboa trees. They both agreed that these were specimens of Archaeopteris.

Archaeopteris is an important plant in the history of the evolution of trees. It belongs to a group called the progymnosperms.  That is a group of trees just a little more primitive than the gymnosperms themselves. And, as you might know, the gymnosperms include all of the modern evergreens; this is an important group of trees in the history of life.

The trail at Kaaterskill Falls is a scenic one for everyone who enjoys the outdoors, but for the two of us, it takes us back through time to an earlier planet Earth which was witnessing the rapid evolution of trees and of forests themselves.

Do you have good photos of geological wonders? Send them along with descriptions and perhaps we will be able to use them in a future column.

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

Brachiopods

The Catskill Geologists; May 25, 2018

Robert and Johanna Titus

If you do a lot of fossil hunting in the Catskills then you probably already know much about what we will be writing this week. But, even if you do, you may well find our column worth reading. It’s about a group of invertebrate shellfish that lived right here. And we mean right here. Look around you. Where you are now was once the bottom of an ocean called the Catskill Sea. That sea takes us back roughly 400 million years ago to the Devonian time period. Now take a look at our photo; it’s a piece of sandstone. Its flat surface is a petrified bit of that sea floor. And, just as it was hundreds of millions of years ago, it is littered with shellfish, now fossils. They are brachiopods. We see them on this rock – right where they lived and right where they died.

These animals, in life, lived within two shells so you might be tempted to call them clams. The similarity to clams is accidental. Brachiopods are a very different group of animals. Their internal, soft anatomy is entirely different from that of clams. Brachiopods are not even mollusks. We have blown up the image of one of these brachiopods in our second photo. Notice that there is a plane of symmetry running down the center of the shell. With clams there are also planes of symmetry but they are found in between the shells, not down their centers. Using symmetry you can always quickly tell apart clams from brachiopods. All this is important because these two groups are the most common fossils found in the deposits of the Catskill Sea. You need to know the difference. With experience that will soon become second nature.

All but one of these fossils belongs to a form of brachiopods called Mucrospirifer. Mucrospirifer shells are categorized by their heavy ridges and those two – tapering left and right – extensions, sometimes informally called “wings.” Mucrospirifer is a very common brachiopod in our region’s marine sedimentary rocks. It enjoyed great success during the Devonian. There is a second species of brachiopod in the upper right corner of our photo. It too has a plane of symmetry running down the center of its shell.

There are more things that need to be explained here. First, notice how many Mucrospirifers are seen on this bit of that ancient sea floor. And also notice that they are all just about the same size. We are guessing that this represents something that is common among marine invertebrate animals. Such creatures commonly begin life as single fertilized cells, zygotes that were cast out by their mothers. Alternatively, they may have been early and primitive larva. But in the end it was all the same; these very young invertebrates drifted with seafloor currents until they detected a suitable ecology and, then and there, they settled to the bottom and began their lives. A group of invertebrates of this sort, all the same size, is called a spatfall.

Another thing about these spatfalls is that they seem to us to be commonly found on very dark shales. Geologists generally assume that dark shales represent a quiet sea floor with a low oxygen content. If so, then much of the success of Mucrospirifer came from its ability to survive in a wide variety of environments, places that other animals found inhospitable.

But, in the end, what is important here is for you to learn about a common form of fossil, typical of our Catskills. Don’t your feel just a little smarter now that you have read our column?

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

Glaciers at the Arboretum

The Catskill Geologists

Robert and Johanna Titus

Have you been to the Mountain Top Arboretum? It’s in Onteora Park along Rte. 23C. The Arboretum was founded only about a quarter century ago and we have been members most of that time. It’s spread out across a couple of hundred acres of land, but the core is where the trees of the proper arboretum are, right by the road. They are young and not all that tall yet, but they are coming along.

We will be taking you there to see the geology from time to time, but let’s make our first visit today. If you visit the Arboretum you will be likely be parking in the lot right next to Rte. 23C. Right across from the parking lot, you will see the entrance to the main arboretum. There is a gate there and you can’t enter without passing through it. That’s where the geology starts.

If you look down, then you will see a flat surface of bedrock (our first photo). Look again and notice how that bedrock seems to have been smoothed out. It almost looks polished; it has been. Now look again and you will likely soon notice a series of long, very straight scratches in the rock. They are, all of them, parallel to each other. We always bring a compass along and we got it out and took some measurements. We found that all those scratches lie on a north-to-south lineation.

We had just begun a journey into the past; we were visiting the Ice Age. All that polishing was the result of a glacier passing across this surface.  The bottom of that moving ice was dirty with sand, silt and clay. The ice pressed all that sediment into the ground and polished that surface. Sanded might be a better choice of words. In any case, it was the ice that produced what we see here. If you look through the gate, you will be looking north. That’s the direction from which the glacier arrived. In our mind’s eyes we could look that way and envision that glacier moving towards us.

We have seen surfaces like this many times before. But what surprised us, and what we want to talk about today was something else. Off on the right side of this outcrop we saw a pair of what are called glacial grooves. So far, we have been talking about cobbles being dragged across the surface of the bedrock. These are very good at leaving striations. But, imagine for a moment that some very large boulders were being dragged by too. You would expect them to be pressed into the ground as much or more as nearby cobbles.

Those boulders, as you would expect, were making something bigger than striations; we call them glacial grooves. Grooves are a lot wider and deeper than striations. But there is something else. Those boulders were being pressed down by the weight of the ice. That tended to hold them in place. But they were also being pushed from behind by the moving ice. For a period of time the weight of the ice did hold these boulders in place, but then the push from behind got to be so great that the boulder skipped forward in a sudden leap. When it “landed,” it created a large crescentic nick in the surface of the bedrock. We call such nicks chattermarks.

This process continued for some time. Every “leap” forward left a new chattermark, all of them nicely nested in the boulder’s groove (our second photo). That’s what we see at the Arboretum and we don’t remember ever seeing any grooves quite as good as these. They are well worth a visit.

There is one problem with today’s story. If the sunlight is just right, then you will be able to see all that we have described. But if the light is wrong . . . then you will see none of it.

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

The Davenport Delta

The Catskill Geologists; The Mountain Eagle

Robert and Johanna Titus

Mar. 23, 2018

Did you ever take a good earth science course – in high school or college? Well, one of the things that commonly comes up is the structure of a delta. Deltas form when rivers or creeks flow into bodies of still water, oceans and lakes. The flowing water currents almost always carry a fair amount of sediment in them. That’s mostly sand, silt and clay. When those currents enter into a lake or ocean they generally slow down. Slow currents can’t carry as much sediment, so a lot of it gets deposited in the form of a delta.

Large rivers, flowing into oceans, tend to form large deltas. Think of the Mississippi Delta. Small creeks, flowing into your town’s skating pond, create small deltas. Big or little, deltas all have pretty much the same basic structure. The advancing front of the delta displays a steep slope that forms the delta’s outer edge. The sediments of this part of the delta display an inclined stratification. Those strata dip toward the lake bottom. The top of the delta receives sediments that are deposited on a flat plane. Those strata are horizontal.

Those inclined strata are called the foreset beds and, on top of them, are the horizontal strata of the topset. The adjacent lake bottom or sea floor, just beyond the foreset, receives a little more sediment, again deposited in flat stratified horizons. These are the bottomset deposits.

Well, in the end, a delta has a flat topset, a flat bottomset and a relatively steeply sloping foreset in between. Here’s the problem; deltas are underwater so we can’t see any of this. But, what if the lake drains, sometime after deposition of the delta? Then that delta would be left high and dry. We can read your minds right now: how can such a thing happen. Lakes don’t drain away, so the deltas will never be visible. Right?

Maybe – or maybe not.

Take a good look at our photo. It was taken just a short distance east of Davenport Center, looking north along Rte. 23. Close to the center of the photo is a house. Notice that behind it, to the left, is a flat surface. Just to its right is a relatively steep slope. At the bottom of that slope is another flat surface (almost hidden by trees). If you didn’t know better you might think that, arrayed right to left, was the bottomset, the foreset and the topset of a delta. But, of course, that can’t be, can it?

Well, if this is not a delta, then it is one remarkable imitation of one. We have a lot of explaining to do, don’t we? That supposed bottomset deposit, is a flat surface that extends quite some distance off to the east. We have done a little exploring there. Whenever we have climbed down to reach this “bottomset” we bring along a barbeque skewer. A what? Yes, a barbeque skewer; it is a very valuable piece of equipment when we are studying ice age deposits.

We drop down onto what we think is an ice age lake bottom and we try to drive the skewer into the ground. If it slides in easily then we know that there are no cobbles or pebbles in the ground. That is typical of lake bottom sediments. We try again with the skewer, and then again and again. If our skewer keeps sliding in, time after time, then we can assume that our flat surface is indeed the bottom of an ice age lake. That’s always a fun discovery. And, better still, this one was a lake with a delta.

Most of the Charlotte Creek Valley was dammed by melting glaciers at the end of the Ice Age. Lakes formed behind these ice dams and so it was that deltas, from time to time, formed in these lakes. We have discovered one of these old deltas. If you have a chance, go there and take a look; see the landscape there as we do.

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

Frozen in time

The Catskill Geologists; The Mountain Eagle; Nov. 30, 2023

Robert and Johanna Titus

Frozen in time is a common enough phrase. It usually refers to people or cultures who have not kept up with changes. Time goes by and changes come along, and those people and those cultures stay the same, stuck in the same old rut. Being frozen in time has a bit of a negative connotation. It happens when we just can’t change with time-or perhaps we don’t want to.

That time-worn old phrase leaped into our minds recently when we were up at the Mountain Top Arboretum. To geologists the notion of being frozen in time has a very different, even a professional meaning. We had been wandering the grounds at the Arboretum when we encountered an outcrop of typical Devonian aged Catskill sandstone. Are you familiar with the Arboretum? We are talking about the southeast corner of what is called the West Meadow. Usually seeing such rock is pretty routine and hardly very exciting, but this was different.

Take a look at our photo. Notice that the strata on the right dip to the right while those on the left dip in the opposite direction. What’s going on here? Well, we were looking at clues and were able to conjure up images of the distant past, a past that had given birth to our sandstone. These left- and right-leaning strata are said to be cross-bedded, actually the technical term is trough cross-bedded. That happens in modern river channels. On the deep, outer side of a wandering stream, the currents flow their fastest. When there are heavy rains, then the stream speeds up some more. It becomes erosional and scours out small channels, troughs, in the channel sands. At the end of the flood those currents slow down.  That’s when the stream loses its ability to carry sediment, most of it being sand, and a depositional event follows. Sand fills in the troughs and is stratified in a fashion that is parallel to those scours – sometimes left leaning, sometimes right.

You wait a few million years, and all this hardens into stratified sandstone. Then you wait a few hundred million years more and that sandstone is exposed by the slow and steady processes of erosion. Well, that sums up what happened at the Arboretum and that is how we saw it. But then we got just a little philosophical. We began to ponder what we were looking at.

We were looking into the distant past. We were looking at the floor of a stream that had once flowed by here, across the top of something called the Catskill Delta. And we were looking at a moment in time. This was, essentially, an instant in time. All that sediment had been deposited right there and right at that moment. If any of those sand grains had a mind of its own, then it would have thought that there was no reason why another flood should not come along, sweep it up and carry it off to the nearest ocean.

And that is, in fact, what usually happens. Almost all grains of sediment are destined to enter an ocean and become part of the sediment there. Go to the Jersey shore and pick up a single grain of sand on the beach. There is a very good chance that your sand grain came from the Catskills and had traveled down the Hudson.

But not with our sand grains at the Mountain Top. They had become “frozen in time.” Their river channel deposits had come to be buried by more sediments – and then even more – thousands of feet more. All of this had hardened into the sedimentary rocks of the Catskills. Our mountains are an ancient delta deposit – frozen in time.

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

What is Bluestone?

The Catskill Geologists; The Mountain Eagle 10-16-18

Robert and Johanna Titus

It would be hard to find a topic more emblematic of the Catskills than bluestone. It’s a stone that has been quarried hereabouts for nearly two centuries. It has mostly been fashioned into sidewalk slabs, but it has a large number of other uses as well. You can probably easily conjure up images of bluestone sidewalks in your mind’s eyes; there are so many of them still around. Then, you can probably also recognize buildings and churches made of the stuff. But just what is bluestone?

Bluestone is composed of large slabs of sandstone. Those sandstones are horizontally stratified, and, because of that, brawny quarrymen were able to excavate it and, using large sledge hammers and chisels, break it into those slabs. These were then shipped off to locations all over the eastern United States. Bluestone sidewalks last very long amounts of time. Also, they were skid resistant when it rained and, we think, very good looking. No wonder they were so popular. Are bluestones truly blue? We have always had a hard time finding bluestone that actually is “blue.” We understand that whatever blue there is comes from some of the clays that make up small components of these sandstones.

But, we still haven’t answered the question “what are bluestones.” Doing that means that we will have to travel back in time about 380 million years and visit the Catskills region as it was back then. It you have been reading our columns then you know that this was the Devonian time period and, back then, the Catskills region was an enormous delta. Rivers flowed across this, the Catskill Delta, and sands were deposited in their channels.

Flowing water picks up sand and moves it along. Depending on exactly where in the channel those flows are, governs just how fast the currents flow. Typically, one side of the stream sees the fastest flow while the other witnesses the slowest. Strata on the fast-flowing side are recognizably different from those of the slow side. We should talk about those deposits in future articles, but our focus today is on the middle of those petrified streams; that’s where the bluestone formed.

The middle of those Devonian streams accumulated those flat lying strata of sands. It was those that eventually hardened into the flat lying strata that make good bluestone. Some of those streams were a lot bigger than others. It was the largest of those streams that accumulated deposits thick enough to form bluestones that were commercially valuable.

Bluestone quarries were developed all across our mountains, but they were especially common in the Eastern Catskills. Quarrying was most active in the late nineteenth and early twentieth centuries. All the old, abandoned quarries are still there and they provide geologists with wonderful keyholes into our mountains’ Devonian past. We enjoy visiting them and exploring what they have to show us.

There still is an active bluestone industry but is mostly in the western parts of Sullivan County.

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

The Davenport Delta

The Catskill Geologists; Robert and Johanna Titus

The Mountain Eagle; Mar. 23, 2018

Did you ever take a good earth science course – in high school or college? Well, one of the things that commonly comes up is the structure of a delta. Deltas form when rivers or creeks flow into bodies of still water, oceans and lakes. The flowing water currents almost always carry a fair amount of sediment in them. That’s mostly sand, silt and clay. When those currents enter into a lake or ocean they generally slow down. Slow currents can’t carry as much sediment, so a lot of it gets deposited in the form of a delta.

Large rivers, flowing into oceans, tend to form large deltas. Think of the Mississippi Delta. Small creeks, flowing into your town’s skating pond, create small deltas. Big or little, deltas all have pretty much the same basic structure. The advancing front of the delta displays a steep slope that forms the delta’s outer edge. The sediments of this part of the delta display an inclined stratification. Those strata dip toward the lake bottom. The top of the delta receives sediments that are deposited on a flat plane. Those strata are horizontal.

Those inclined strata are called the foreset beds and, on top of them, are the horizontal strata of the topset. The adjacent lake bottom or sea floor, just beyond the foreset, receives a little more sediment, again deposited in flat stratified horizons. These are the bottomset deposits.

Well, in the end, a delta has a flat topset, a flat bottomset and a relatively steeply sloping foreset in between. Here’s the problem; deltas are underwater so we can’t see any of this. But, what if the lake drains, sometime after deposition of the delta? Then that delta would be left high and dry. We can read your minds right now: how can such a thing happen. Lakes don’t drain away, so the deltas will never be visible. Right?

Maybe – or maybe not.

Take a good look at our photo. It was taken just a short distance east of Davenport Center, looking north along Rte. 23. Close to the center of the photo is a house. Notice that behind it, to the left, is a flat surface. Just to its right is a relatively steep slope. At the bottom of that slope is another flat surface (almost hidden by trees). If you didn’t know better you might think that, arrayed right to left, was the bottomset, the foreset and the topset of a delta. But, of course, that can’t be, can it?

Well, if this is not a delta, then it is one remarkable imitation of one. We have a lot of explaining to do, don’t we? That supposed bottomset deposit, is a flat surface that extends quite some distance off to the east. We have done a little exploring there. Whenever we have climbed down to reach this “bottomset” we bring along a barbeque skewer. A what? Yes, a barbeque skewer; it is a very valuable piece of equipment when we are studying ice age deposits.

We drop down onto what we think is an ice age lake bottom and we try to drive the skewer into the ground. If it slides in easily then we know that there are no cobbles or pebbles in the ground. That is typical of lake bottom sediments. We try again with the skewer, and then again and again. If our skewer keeps sliding in, time after time, then we can assume that our flat surface is indeed the bottom of an ice age lake. That’s always a fun discovery. And, better still, this one was a lake with a delta.

Most of the Charlotte Creek Valley was dammed by melting glaciers at the end of the Ice Age. Lakes formed behind these ice dams and so it was that deltas, from time to time, formed in these lakes. We have discovered one of these old deltas. If you have a chance, go there and take a look; see the landscape there as we do.

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