We are Civil War buffs so we very much enjoyed Richard Heppner’s recent article about Ulysses Grant’s visit to Overlook Mountain (WT, 3-15-18). But, what caught our attention the most, was the old picture that he included (reproduced here). It shows the very top of Overlook Mountain as it was during the 1870’s, when then President Grant made his visit. Notice the prominent cliff lying right in front, or to the immediate south, of the Overlook Mountain House Hotel. Next, look behind that cliff. The landscape there, where the hotel once stood, is an awfully smoothed off surface. It even looks to have been planed off by some gigantic carpenter’s tool. It’s an interesting landscape and it deserves the attention of a geologist.
That old picture took us back 22 years to the very first “On the Rocks” column. When you are writing a first column, you want to get the attention of your new readers. That column took our new readers to the top of Overlook. But in 1996 you could not see the landscape as it is portrayed in its 1870’s manifestation. Still, that long-ago column got it pretty much right. Good hiking weather is coming up soon enough. Maybe you should climb Overlook and see the geology up there for yourself.
If you climb to the top of Overlook, look around and you will soon find a number of locations where the bedrock pokes through the thin soils. As often as not, that bedrock will display a planed off, even sanded, appearance. You will find long straight scratches on those surfaces. Geologists call them glacial striations; they recall the passage of the ice across the top of Overlook — probably more than 20,000 years ago. If you bring a compass along, you can measure the direction that the glacier was heading. It was a little west of south in 1996; and it probably still is.
Those polished and striated surfaces extend right under the Overlook fire tower. The tower was not open 22 years ago but it is now. Climb to its top and gaze out to the east. In your mind’s eye, witness the Hudson Valley fill with ice. You watch as the glacier moves south below you and curls around the bend made by Saw Kill Creek. It advances up the Saw Kill Valley. You can “see” all this from the top of the tower. Next, that glacier rises up to the level of the fire tower, itself, and then it keeps going for a thousand feet, or more, higher. The 1996 column marveled over how the glacier had reached up to the tower’s elevation which is 3100 feet above sea level. We still have just as much wonder when we stand atop the tower today.
But, what about that cliff? It’s an obvious feature in the 1870’s picture, but only a little of it could be easily seen in 1996; the rest was “buried” in the trees. Geologists, long ago, figured out the meaning of such south-facing cliffs. They are called “plucked cliffs.” The glacial ice that had passed across the top of Overlook, formed a bond with the bedrock. It’s the kind of bond that your tongue will form when it touches the bottom of an ice tray (Do you remember the Jean Shepherd story of the little boy and the frozen parking meter?).
But a glacier is not a tongue and Overlook Mountain is not an ice tray. The glacier did form a strong bond to the bedrock and, as it moved onward to the south, it yanked, or plucked, great masses of bedrock out of the mountain. That left the cliff as it was portrayed in the old picture. This cliff faces the direction that the glacier was moving.
This historic image of Overlook Mountain is a classic example of the sort of old illustrations that geologists are eager to look at. All during the 19th century many of our landscapes had been cleared, mostly for agricultural uses, but also for other reasons — like hotels. The landscapes became uncovered and geological features were uncovered just as much. Since that time, our northeast has become the most reforested area anywhere on the globe (or so they say). We geologists applaud reforestation and hope it spreads. But it’s a mixed blessing for us; reforestation has buried a lot of good geology under the trees. Old illustrations thus become very helpful. They let us see things that have been otherwise lost. Give Overlook a climb sometime soon and see these things for yourself.
Contact the authors at email@example.com. Join their facebook page “The Catskill Geologist.”Read their blogs at “thecatskillgeologist.com.” The 1996 Woodstock Times column was posted as a blog on Oct 19, 2017.