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A visit to Lester’s Cave

The Catskill Geologists; The Mountain Eagle; Aug. 2, 2019

Robert and Johanna Titus

We are guessing that virtually all of you have visited Howe Caverns. It’s the premier tourist attraction of our region. But there is a relatively new attraction in the same area

and we think that you will enjoy visiting it. That’s the Cave House Museum of Geology and Mining. Take Rte. 7 east from Cobleskill and turn left at Cave Road and left again at Blowing Rock Road. Drive a quarter mile and, presto, you are there.

You will see what’s left of Lester Howe’s old hotel, Cave House. It had been in serous disrepair but is now on its way to restoration with the help of the Callanan Industries. Howe opened the hotel during the middle of the nineteenth century and its guests were mostly people who came to see his cave. There used to be a larger hotel building next door but that one built of wood and it, long ago, burned down.  Cave House still needs lots of work but is on its way to becoming a genuine museum with a focus on the local geology. Staffed by dedicated volunteers, the museum is open every other summer Sunday. Check their facebook page before you go. When you get inside you can view a host of geologic specimens, most of them are local rocks, minerals and fossils. These have been donated by local geologists.

But here is the best part. Cave house is located quite some distance from the modern entrance to Howe Caverns.  But in Lester Howe’s day the entrance was located right beneath the hotel. Guests would step outside, climb down a staircase and be led into and through the cave. You can do some of the same today; at least you can see some of the old cave.

The walls of the cave are composed of limestone, most of it specifically belonging to a unit called the Manlius Limestone. These rocks take us back almost 420 million years ago. The rocks are layered; we call each horizon a stratum; this is a stratified rock. Such limestones accumulated in a very shallow tropical sea. You would have to go to the Persian Gulf to see this type of sea today.

If you did visit the Persian Gulf and walked its beaches at low tide, you would see just the sorts of sediments that harden into strata like the Manlius. In fact, starting a half century ago, many geologists did just that They studied those sediments and compared them to the Manlius. What they learned about the Manlius was something of a scientific breakthrough.

We remember being shown Cave House many years ago, when it was literally falling down, so it is such a pleasure to see it going through this rebirth. We applaud all those involved in this project. There is more for us to write about here so we will return to this topic again – soon. We hope you will visit.

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

A visit to the side of a road

The Catskill Geologists; The Mountain Eagle; July 26, 2019

Robert and Johanna Titus

We try hard to get columns out every week here in the Mountain Eagle. The secret is getting good photos to work with. Once we have the right picture, it is usually easy to put together an interesting geological yarn. It’s such a blessing for us that today’s smart phones come equipped with cameras and good ones at that. When we were younger, we could have never dreamed of taking pictures with a telephone, but we depend on that now. Wherever we go, we keep a sharp eye out and whenever we see something good, we just pull out our phone” and shoot. Pretty soon, you are reading about it.

That brings us to today’s yarn. One recent Tuesday evening we were on our way to WIOX in Roxbury when there it was – some fine road work. We love road work; so often it brings to light an exposure of bedrock. Take a look at our photo. It was taken alongside the Susquehanna Turnpike, a few miles west and uphill from the village of Durham. Look again, you might not guess it but there is a lot of geology in there. We geologists always start at the bottom and work our ways up from there. That takes us from the oldest to the youngest – a trip through time.

In this photo the oldest strata are of typical Catskills bedrock, a horizon of sandstone. You might prefer to call this rock Catskills bluestone, it doesn’t much matter. In either case, we looked at the rock and were transported about 385 million years into the past. There we found ourselves in the channel of a substantial river. That’s where the sand of this sandstone had been originally deposited. We walked up to the exposure and held our hands out. We could feel the powerful river currents that had once passed by here. Then they slowed down and then they stopped. This stream had jumped its channel; right here it would never flow again. That’s not as unlikely as it sounds. Streams don’t flow on forever in one channel; they do alter their courses and, long ago, that happened right here. Those sands came to be buried under more sediments, then more and then thousands of feet more. They would soon begin a process of compaction that would, with time, turn them from sediments into the bedrock we see here.

What happened to all those other sandstones – the ones that used to lie above? The answer is that they were all eroded away. We looked up into the sky and “saw’ thousands of feet of sedimentary rock rising above us. And we knew that they had, again so long ago, eroded away. And the last of that erosion is represented by the platform about halfway up our photo. That surface is important. Once, out of the north, an erosive glacier had ground its way across it.

Our photo shows that, above that erosion surface, lies a few feet of – what? – soil? Actually no, this is something else. It’s a few feet of earth that is called a ground moraine. A ground moraine is a relatively thin horizon of material that dropped out of a melting glacier at the end of the Ice Age.

We had stopped along the side of the road, attracted by something that looked of interest. We had taken a photo and had found ourselves another good yarn. This yarn involved an ancient river and a passing glacier. Our yarn was spread out across hundreds of millions of years. It is a good yarn.

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

A leaning tree?

The Catskill Geologists by professors Robert and Johanna Titus

The Mountain Eagle ; July 19, 2019

Take a look at our photo. Do you see anything of note? Well, if you don’t then you don’t have the trained eye of a geologist. We think you can be forgiven for that, but let’s work on it. After all, that’s what our column is supposed to be all about.

This photo was taken down at the Roosevelt Estate in Hyde Park. We go there for events all the time, so we have learned a lot about the area’s geology. The estate is spread out across the top of an ice age delta and the photo shows the edge of that delta. You probably would never guess it, but the whole bottom of the Hudson Valley was once a great, deep glacial Lake called Lake Albany. All of Hyde Park lies on a delta of that lake. The top of any delta is a very flat surface called a topset. The edge of the delta is a steep slope called the foreset. Our photo focuses on the boundary of the two. The topset is spread out to the right and all of the library buildings lie upon it. The foreset drops off quickly to the left.

A typical delta is composed of cohesive silty sediments and, with its steep slope, the foreset can be a very unstable landscape feature. Delta foresets commonly display what are called rotational slumps. Large mases of the cohesive silt break loose along curved faults and rotate downhill. You might think of this sort of thing as a slow landslide. Take a look at our second illustration. It shows a mass of earth sliding in a clockwise motion down a curved fault line. At the top of the slide trees lean backward; at the bottom, they sometimes lean forward. Now, look at our photo again. Do you see something that you didn’t minutes ago?

So, why are we writing about a feature on the east side of the Hudson River? This column is supposed to be about the central Catskills; isn’t it. Well, again. We want you to have a trained eye, alert to all sorts of geological features that you might be passing on a routine day. Have you ever noticed a leaning tree? Even if you did, did you know what it might portend? Could you possibly have suspected a landslide hazard?

And, in this case, there is something very important: is there a danger that the Roosevelt mansion, Springwood, might break loose and slide downhill? Our photo was taken just a short distance north of Springwood. We were certainly concerned when we first visited so we explored the area. But the news was good; we found no leaning trees close to Springwood and only a relatively few in the vicinity. But there was more: we found few, if any, leaning trees at the bottom of the foreset slopes. It has been our experience that with dangerous slopes, the trees at their bottoms come to be shoved forward. Take another look at our second illustration.

So, in the end, we are not overly concerned about the safety of Springwood and the whole of the Roosevelt Library and Museum. But you can never be entirely certain about these things. You might take a look at the trees where you live.

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

Some shiny rocks in Plattekill Clove

Robert and Johanna Titus

The Catskill Geologists; The Mountain Eagle; July 12, 2019

It’s not unusual for us to hear from one of our readers. That’s, after all, why we publish our email address at the bottom of each article. It is also not unusual for them to send us a photo of something worth writing about. That happened recently when someone we know as “Catskill Bear” sent us this week’s photo. Mr. Bear found this rock along the road in Plattekill Clove. He was most curious about the striated and shiny surface he saw on it. That makes up the whole left side of the rock in his photo.

Well, we recognized what this was right away, but we still needed some help on it, so we contacted our friend, Dr. Charles (“Chuck”) Ver Straeten at the New York State Museum, and asked him about it. Chuck is a geologist who knows just about everyhing there is to know about the Devonian age stratified rocks of the Catskills so we knew he would be able to help.

We already knew the fundamentals: what our reader had found was a shiny surface called a slickenside. We had been transported back to a landcape called the Catskill Delta. It was about 385 million years ago, the middle of the Devonian time period, and that delta was spread out across all of today’s Catskills. There was a tropical climate here way back then. And many geologists think that the climate was seasonal with dry months and wet months every year. Much of the delta was blanketed in a common soil type called a vertisol.

Scientists know a lot about vertisols because they exist today. They possess clay minerals that shrink during the dry seasons and expand when they get wet. That creates a back-and-forth motion within the soil. One mass of soil expands and slides past the other during the wet season. It contracts and slides past the other mass in the following dry season. The result of all this are soil slickensides.  And that is exactly what Catskill Bear had found.

But there is more; it seems like there is always more. Chuck has, himself, been interested in Devonian soil slickensides. He has noticed that they are concentrated in certain horizons within Catskills stratigraphy. There are stretches of Catskills stratified rock where they are common and other stretches where they are not. He wondered why.

It’s common for Nature to present scientists with patterns like this. Nature is challenging us: where there is a pattern, then we must seek to learn why. If we meet the challenge and answer that question, then we are likely to have discovered something. It’s a common way that science works, and a fun way.

Chuck developed a hypothesis to explain this. A scientific hypothesis is a tentative explanation. It has not been properly tested and thus has not been proved – not yet. Chuck has long understood that volcanic eruptions can produce the clay minerals that promote expansion and contraction in vertisol soils. His hypothesis is that explosive Devonian eruptions in New England might have showered our region with ash that, potentially, could have been be altered into those “shrinking clays” and thus subjecting local soils to seasonal expansion and contraction. Slickensides would be concentrated in certain stratigraphic sequences because those represent times of volcanic activity. Sounds good, doesn’t it? But this is just hypothesis; it still needs work.

In the end, slickensides are among many, many phenomena that we routinely encounter in the Devonian strata of the Catskills. You too can learn about them. With time, you learn to notice these things. They speak to you about the past. You have become more knowledgeable. Your hikes in the Catskills become such different, more enriched, experiences. And it all starts from reading these columns.

Have you found some interesting geology? Write us about it. We are at randjtitus@prodigy.net. Join our facebook page “The Catskill Geologist.” Read our blogs at “thecatskillgeologist.com

The Devonian at Pratt’s Rock

The Catskill Geologists; The Mountain Eagle, June 28, 2019

Robert and Johanna Titus

We have been doing a series of columns about Pratt’s Rock, which is, of course, in Prattsville. The stone carvings up there have, for 150 years or so, been attracting visitors. Today Pratt’s Rock is showing its age; it needs more than a cleaning; it needs a full refurbishing and that is what is being planned. Renowned landscape architect, Michael Van Valkenburgh, has been recruited to play a leading role. We have been wanting to contribute to all this by describing the geological heritage of the site. We think that’s an important aspect of the history of Pratt’s Rock and Prattsville itself. In our last two columns, we have described the ice age history there. That was only about 15,000 years ago. But today, we go back almost 380 million years to visit what geologists call the Devonian time period. All of the stratified rocks at Pratt Rock are as they were when first deposited during the Devonian Period.

Actually, we will start off by visiting what was intended to be Colonel Zadock Pratt’s crypt and then, from there, we will travel into that Devonian past. Take a look at our photo. You will see the Pratt chamber opening on the lower left. Our understanding of the story is that Colonel Pratt would have been interred there except that it started leaking. Just above that chamber, are some curious strata. Do you see how they are inclined to the right? We think that most local geologists would recognize this as being the left shore of a Devonian river. It needs a name and we love to name things; let’s call it the Pratt River.

   April 3, 379,998,163 BC – We are the mind’s eyes, and we have gone back those almost 380 million years and we are hovering above what will someday be Prattsville. We slowly turn a full 360 degrees and survey the landscapes below. We are just a few hundred feet above what has been called the Catskill Delta. Off to the east, a hundred miles or so, rises an enormous mountain range. These are the Acadian Mountains. They tower above what are the Berkshire Mountains today.

The Catskill Delta lies spread out before and below the Acadians It passes beneath us and continues perhaps another hundred miles to the west. Out that way is a broad shallow ocean, called the Catskill Sea. We turn another 360 degrees and appreciate how flat it all is. As far as we can see, there are rivers, an endless number of them. This is not surprising; large deltas always display large numbers of rivers. They are called distributaries and they always fan out across a delta. These rivers eventually “distributed” their waters into the distant Catskill Sea,

We, the minds eyes, drift downwards and we approach the nearest of these distributaries; it’s the Pratt River. We hang in the air, just a few feet above its waters. We look upstream and downstream. On this day there is only a lazy current slowly passing by. It is high noon on a sunny day, and we can see to the bottom. Down below are what we think are fish. But they are clumsy looking animals, thickly armored with heavy bones. Fish have only recently evolved into such river ecologies and they are not yet very good at it.

Below the fish, on the stream bottom, are scores of three-inch long clams. They sit there, all of them facing upstream. They face into the river currents and are able to sift out bits of biologic matter. This is, for them, food. Similar clams still live in Catskill lakes.

The riverbanks are densely populated with trees. But they are all so primitive looking. Long straight trunks rise up about 20 feet. There are no branches, but a strange foliage crowns each tree. It’s hard to find the right words to describe these crowns. There are no flowers, no seeds, no nuts; there are not even proper leaves. There are “appendages” that are green and photosynthetic; there are others that are reproductive. Those have black spore-producing bodies dangling from them. We look again, far and wide; there are no broad-leafed trees; neither are there any evergreens. This is a primitive forest, populated by primitive trees.

On the forest floor are some relatively familiar creatures We see millipedes, centipedes and spiders. Then we spot silverfish. These six-legged invertebrates are among the world’s most primitive insects. But there are no mammals, none at all. Neither are there any reptiles or even amphibians. There are no birds high above, singing in any of these “trees.” It is a quiet day and there are no sounds whatsoever. The silence is unnerving.

All this is the famed Gilboa Forest. It is evolution’s first-ever attempt at forest ecology, and it once grew and thrived right where Pratt’s Rock is today. Our journey through time has been a journey through the history of life itself.

Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com.” But mostly, go and visit Pratt’s Rock sometime this summer.

A glacial lake at Prattsville

The Catskill Geologists; the Mountain Eagle, June 21, 2019

Robert and Johanna Titus

We are pleased to hear that Pratt’s Rock will be refurbished. A sizable sum of money has been set aside to repair the site in the “same spirit of Zadock Pratt.” Pratt’s Rock, long regarded as the “Mt. Rushmore of the east,” has always drawn thousands of people to the town. They walk up the trail there and explore the sculptures. It is hoped that the numbers of tourists will increase with the restoration.

We have climbed the rock and have always enjoyed visiting but, for us, there is more there than just the carvings. Last week we wrote about the effects that advancing glaciers had on the site during the Ice Age. We saw that the steep slopes of Pratt’s Rock were the products of the ice passing across this hill and plucking masses of rock out of the ground, leaving a near cliff behind. Much of Schoharie Creek displays similar cliffs and they formed in the same manner. But glaciers did not just advance; they also melted back. When they did, they left other ice age features.

Take a look at our first photo. It shows the top of that plucked cliff. That advancing glacier passed across it and smoothed it into form we see today. A lot of rock was yanked out of the ground, leaving a cliff behind. We talked about all this last week. But look again; in the distance is a flat valley floor. That should simply be a floodplain. Right? Well, wrong; this is the floor of a glacial lake that was once down there. It has a name; it is Glacial Lake Grand Gorge.

Here’s what happened: Something called the Schoharie Creek Valley glacier advanced southward almost to Lexington. It came to a halt there as the climate started warming up. Great masses of earth had been bulldozed toward Lexington and left behind when the ice melted back. This was sediment that served as an earthen dam so that the retreating glacier left lake waters. Lake bottoms accumulate great quantities of silt and clay as lake deposits. Lake bottoms are always flat and that is what we see in the distance from the top of Pratt’s Rock.

If you go down there you can prove this for yourself. Bring a barbeque skewer and try to drive it into the ground. Throughout most of the Catskills skewers won’t go very far into the ground; they will hit rocks or pebbles. But down there, east of Prattsville, those lake deposits are all silt and clay; a skewer will always slide easily into the ground.

This was a big lake and deep too. Take a look at our second illustration. The lake level is thought to have been about 1,600 feet in elevation. Prattsville is at about 1,165 feet so the lake was more than 400 feet deep.  When we stand atop that ledge, we always see the image of Lake Grand Gorge spread out before us; it’s quite the sight.

We hope that, as part of renovations, a path to this ledge will be marked. Perhaps a placard can be placed there with an explanation of this ice age history. It’s an important part of the Pratt Rock heritage.

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

A glacier at Pratt Rock

The Catskill Geologists; The Mountain Eagle May 14, 2019

Robert and Johanna Titus

We were happy to read in the Mountain Eagle of plans for the upcoming restoration of Pratt’s Rock. It’s quite an unusual location; it’s been there a long time and does need an upgrade. We look forward to seeing what will happen, and we hope, when things are done, there will be some appreciation for the geological heritage of this fascinating site.

Had all gone to plan then Zadock Pratt would have had quite the Mausoleum up there, but that did not happen. Nevertheless, Pratt does still have a most impressive monument. Probably most all of you have visited it. Many of you have climbed up and seen closeup the carvings that are there. There is still a chamber where Pratt planned to be buried. Then there is the poignant image of Pratt’s son George who died at the Civil War’s Second Battle of Bull Run.

None of this would have or could have been if there had not been such a steep slope there to begin within. Take a look at our first illustration; it shows a topographic map of Pratt’s Rock. Can you “read” contour lines? Then you will recognize the steep Pratt Rock slope from the closely spaced contours. It’s nearly a cliff and it faces the valley of Schoharie Creek which flows through Prattsville. Ledges of Catskill sandstone tower above the valley. A ledge is just a ledge, isn’t it? Well, not where we come from; we are geologists and we know there is a deeper story here

We hike up to the carvings and then continue onwards to a ledge that offers a fine view of the valley. See our second illustration, a photo of that ledge. Notice the smooth surface and the sharp drop-off of the ledge; there is a cliff there. Less obvious, but quite important, are the scratches on that surface. There is a lot of ice age history here. We look and we see what is called the Schoharie Creek glacier passing by. It has flowed south, swelled up to fill the valley and passed across this sandstone. The ice carried a lot of sand with it, mostly concentrated at its dirty bottom. That sand acted as sandpaper and produced the flat surface. There was more, the glacier carried cobbles and boulders along with the sand. They were dragged across this surface and that produced those scratches which geologists call striations. Knowing this, now you can see that they parallel the glacier’s movement down the valley.

What about that cliff? That’s all part of the same story. Glaciers can be sticky. A glacier, when it passes across a mass of rock such as this, forms a tight bond with it. The glacier continues its journey south, it exerts a tug upon that rock. It is quite possible that the tug will break loose a mass of rock and yank it loose. That’s what happened here. There is nothing unusual about this; we geologists see such things frequently. It has a name; we call it glacial plucking. We stand at the top of this cliff, look down the valley and know that somewhere down there is all that missing rock, buried in the floodplain.

Well, the story we have just related, goes a long way to explain how it was that Pratt’s Rock came to be. It started out as an ice age feature. But there is a lot more to this story. Let’s continue next week.

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

A hike to South Mountain

The Catskill Geologists; The Mountain Eagle, June 7, 2019

Robert and Johanna Titus            

The hiking season has arrived for the Mountain Top Historical Society (2019). The two of us have been members for decades and have long enjoyed going exploring with them. On Saturday, that’s tomorrow, renowned hiker Bob Gildersleeve will be leading a trek to the edge of the Catskill Front at South Mountain. That’s a remarkably scenic location that rises above Kaaterskill Clove and overlooks the vast expanse of the Hudson Valley.

It looks like most of the hike will be on or near the Blue Trail. That path rises up the slope just south of the old Catskill Mountain House Hotel site. That will take the hike up a slope that was carved by the glaciers of the Hudson Valley glacier. Participants can expect to see views of the valley from the tops of sizable cliffs. Today’s scenery is spectacular but try looking at the alley and see it filled with ice! That was perhaps 16,000 years ago.

The Blue trail will pass by ledges of rock called the Twilight Park conglomerate. That’s a thick mass of petrified gravel and cobbles. It will take us another 380 million years into the past. You look at the strata to the west of the trail, and then turn to the east. Now, rising high above you, towers the image of an enormous and ancient mountain range, the Acadian Mountains. Those cobbles and gravels formed as a mass of sediment, that was transported down the old mountain slopes, mostly by gravity. That range is nearly gone. Only the Taconic Mountains, across the valley, remain as remnants of what once were colossal mountains, rising between 15 and 30 thousand feet above the eastern horizon.

The trail and its environs are littered with enormous boulders, most of them left behind by the actions of glaciers. Does Druid Rack sound interesting? How about Boot Jack rock or Sphinx Rock? They are all there, near or along the trail. For the most part, they were yanked out of the ground by passing glaciers and then dragged to where we see them today.

This is a classic trek; it’s been a tourist destination for generations. People have been hiking these pathways since the early 19^th century. Visitors to the old hotels enjoyed these trails. Countless postcards were made here. We remember our first visit and the impact it had on us. Have you been? If not, then you should not miss this hike; you will not forget it.

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

Looking into the future

The Catskill Geologists

Robert and Johanna Titus

We frequently travel about in the Catskills, and we are always on the lookout to find a new topic for one of our columns. One day, recently, we were approaching Mt. Utsayantha from the northeast on County Rte. 14. On the mountain’s slope, rising in front of us, we noticed a fairly nondescript mountainside feature. Take a look at the left center part of our photo. You will see what is sometimes called a niche. That is, there is a depression in the side of the mountain.

Well, “so what,” you might ask, “big deal, what is there to get excited about?” And you would be right; this is not an especially big deal; it is indeed just a depression in the slope. But we are geologists, and we are writers. We are always looking for an angle. After all, we have to send off a column almost every week.

We started taking this image and projecting it into the future, of course we mean the distant geological future. What, we wondered, would happen if another ice age came along? Our niche in the mountain would soon fill up with snow. And that would initiate a sequence of very predictable events, typical of the latest chapter of an ice age.

First that niche would accumulate thicker and ever thicker amounts of snow. Then the thickening snows, under the influence of their own weight, would start compacting. The snow would be squeezed down into a material that would resemble the packed snow of a snowball. Geologists call that material “neve”. But the process would not stop there; the compacting would continue until the neve’ would harden into genuine ice.

Once enough ice accumulated in the Mt. Utsayantha niche, it would start to become dynamic. Ice can flow like a great rigid mass of water. Its flow will be very slow, but it will move. It has become a glacier, in fact it has become an Alpine glacier, at least a future Alpine glacier.

We had slowed down but now, intrigued, we pulled over, got out and stared up at our Alpine glacier. Usually, we gaze into the past but this time we found ourselves looking into the distant future. We had traveled to a time when the Catskills had come to resemble the Alps of today’s Switzerland.

When will this future Switzerland descend upon the Catskills? We don’t know; we haven’t gotten any of the ice age geologists that we know, to commit to a precise prediction. But current ice age theory argues that glaciations occur in cycles that recur about once every 100,000 years. So don’t hold your breath. It gets worse; Alpine glaciers don’t form until late in ice age chapters. After all the ice, everywhere else, has melted away then the cold mountaintops become active and Alpine glaciers form.

That happened in the past. At the end of the last ice age, Alpine Glaciers formed atop the highest peaks of the eastern Catskills. The best example that we know of are found at North Point, near North Lake Campground and to the south at Overlook Mountain. Another very fine Alpine peak is Hunter Mountain.

But why didn’t Mt. Utsayantha develop some Alpine glaciers the last time? It may be that the mountain is just not tall enough. It reaches an elevation of 3,200 feet; the others are just a bit taller. So, sadly, Mt. Utsayantha may not be tall enough the next time. But we can dream.

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

Something called planar cross beds

The Catskill Geologists; May 18, 2018

Robert and Johanna Titus

We would like to get you to take closer looks at the rocks you find yourself passing by. We do it all the time. When we are out driving, we pass outcrops along the sides of the roads. It takes a very well-trained eye to see anything at 55 miles per hour, but it can be done. If you are like so many of us, then you will find yourself out hiking in the Catskills. That’s when we want to help train your eyes to see what has always been there, right in front of you. Let’s do some of that today.

Take a look at our photo; it’s a close-up view of some very typical Catskill strata that we took in the western Catskills. It’s something you might see almost anywhere in our mountains. Notice the structure of the strata. There is an obvious horizontal line running across the photo, starting about halfway up. The strata above that line are all horizontal while those in the lower half are sharply inclined. What is going on here?

We always draw a parallel between what we see in the rocks and what we see on roadside signs in a foreign country. Perhaps you have driven through Quebec and have seen signs written in French. Unless you know French you can’t tell what the sign is trying to say. It’s much the same with the strata of sedimentary rocks. The strata in our photo seem to be trying to speak to you, but you have to be able to read rocks in order to find out what they might be saying.

It must be obvious that the strata in the lower half of our photo are telling a different story from those above them. Indeed they are. We need an English/Rock dictionary, don’t we? On one page would be a photo and on the opposite page would be its translation into English. Well, they don’t publish English/Rock dictionaries so we will just have to get along without one. Let’s give it a try.

The strata on the lower half of this photo display what is called planar cross bedding. Each stratum is inclined to the left and all of them are piled up on top of each other. This records a day in the history of the old Devonian age Catskill Delta. We are at the bottom of a stream that flowed across the delta, perhaps 385 million years ago. There had recently been some sort of a flood event and fast flowing water currents had been carrying a lot of sediment. But that flood event was coming to an end and the currents were slowing down. They were losing speed and losing their ability to transport sediment.

That sediment, most of it being sand, was dropping to the river bottom and forming a dune of sorts. More currents, carrying more sand, rose up over the “dune” and deposited sediment in the form of those left sloping strata. Each represented a moment of deposition. That moment was followed by another and then still another until the whole sequence came be as you see it.

There was a momentary return of high speed flow and that eroded the horizontal line which you will see, cutting across all of the planar cross beds. Normal stream conditions then returned and all of those horizontal strata came to be laid down to complete the sequence. Millions of year passed and those sands hardened, petrifying into sandstone. Then hundreds of millions of years passed and the sequence was exposed by processes of erosion and photographed by us.

Keep an eye out and you too will see things like this

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