December 2023

Ripple marks

The Catskill Geologists

Robert and Johanna Titus

A few weeks ago, we ran a column about bluestone sidewalks. Those are sidewalks composed of Catskill sandstones, quarried, cut and split to make slabs that make very fine sidewalks — at least they used to. When cheap, good quality cement came along the bluestone industry  began a long slow decline. That’s too bad; bluestone is the stuff of good stories in geology.

We are going to talk some more about these things this week. We are going to talk about bluestone slabs and bluestone sidewalks – again. But this week, let’s pursue a different angle. There are bluestones and then there are bluestones. Some are just a lot more interesting than others; some tell some pretty interesting stories.

Take a look at our photo. It is a bluestone sidewalk slab from East Main Street in the village of Earlville, located a bit northwest of the Catskills and a bit southwest of Utica. This is not your typical bluestone slab; it is covered by some very striking features. They are called ripple marks. Ripple marks are identified when the surface of the bluestone is — well –rippled. Ripples are very low ridges on the surface of the rock. They are all parallel to each other. But there is more. Notice that the slopes of these “ridges” are asymmetric. The left sides display gentle slopes while the right sides are steep. Those are scientific clues, important clues about how they formed. That asymmetry tells us that the petrified sand which makes up the ripples, was deposited under the influence of currents.

These are called current ripples. They take us back to the Devonian time period, perhaps some 380 million years ago. Our region was, back then, part of something called the Catskill Delta. That was an enormous delta spread out below a great range of mountains that was located in what is today northern New England. Like any great delta, this one was crisscrossed by numerous streams, big and small. Each stream had currents, flowing downstream within them.

That gets us back to those ripples. The currents of those streams picked up sand and carried it downstream. Typically, much of that sand was moving across the stream bottom. It was also being sculpted by the currents into asymmetric ripples. The steep slopes faced downstream. In the case of our ripples from Earlville, downstream was to the right of the photo.

Now, don’t you see, our bluestone slab has become so much more interesting. It transports us to the bottom of a Devonian age stream, flowing across an ancient delta. The currents are not especially powerful, but they do move along at a clip strong enough to carry a lot of sand. Most bluestone slabs formed this way but, with this particular slab, the evidence is so much more convincing.

This slab was not alone; there were a number of them on that Earlville sidewalk. That allows us to read the mind of the man who built this. He must have had an inkling of what ripple marks were, and when he selected the slabs he wanted for his sidewalk, he had a strong preference for rippled ones. This is a work of art.

And that is how we would like you to start seeing these sidewalks. There aren’t all That many of them left. You should start becoming aware of them, especially the rippled ones.

Contact the authors at randjtitus@prodigy.net. Let them know where you have seen rippled sidewalks. Join their facebook page, “The Catskill Geologist.”

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.”