We are going to visit the site of the Rosendale Trestle again this week. When we first went there on May 28 we found a remarkable geological phenomenon and we would like to share it with you. We hope, from that May column, that you remember that the Rosendale Trestle dates back to the late 19th century when it carried trains across Rondout Creek. Today it is the centerpiece of the new Wallkill Rail Trail. The trestle had, long ago, fallen into disrepair, but it has been renovated and you can walk across it and take in a wonderful view of Rondout Creek. We wrote about that view in the May column.
You might also remember that to get there you take Rte. 213 through Rosendale, pass beneath the trestle, and then turn right onto Binnewater Rd. Soon you turn left into the lime kiln parking lot. You have to get out, cross the road, and hoof it up a gentle slope on the Rail Trail right-of-way, heading uphill toward the trestle. Did you follow that? Google Maps will help.
Well, back in May, we were doing all that when our attention was attracted to a fine outcropping of limestone that rose, to our left, high above the old railroad line. That was the Helderberg Limestone. It dates back to early Devonian time making it about 400 million years old. Associated with the Helderberg Limestone, and below it, is a separate type of rock: dolomite. Those strata belong to a rock unit called the Rondout Dolomite. That lies just beneath the Helderberg. Limestone is common type of rock composed of calcium carbonate (CaCO3). Dolomite is composed of calcium-magnesium carbonate (CaMg,CO3), making it a close relative of limestone. But the Rondout is a special type of dolomite; it has just the right amount of clay in it. That makes it suitable for the manufacturing of what is called “natural cement” or “Rosendale cement.” It was good stuff; more than a century ago there was quite an important industry built up around it. People mined the dolomite and turned it into cement.
Well, we didn’t realize any of this while we were first walking up to the trestle. How could we? We had never been there before. But soon our attention was directed to something in that mass of limestone in the cliff above us. But there was more: take look at the photo above. You will see huge blocks of limestone that have apparently collapsed. We thought that we were looking at an ancient cave-in. Perhaps there had once been a cave cutting through the limestone. Limestones frequently have caves in them. And, like so many others, such a cave might have experienced a collapse. Its roof may have simply fallen down. Again, this is the sort of thing that does routinely happen with limestone caves.
It was a perfectly fine explanation but we were in no position to confirm or deny this notion. That sort of idea, in science, is called a hypothesis. That’s sort of an informed guess, and it does not, by itself, carry much weight. A hypothesis has to be confirmed with the close scrutiny of all the evidence that can be gathered. But, where would we get that evidence? Well, we are different from most people; we have a facebook page devoted to this sort of thing. We operate a page called “The Catskill Geologist” and it currently has about 400 members, many of whom know a lot of geology. We just posted our image and waited to see who would answer.
It didn’t take long; we have such accomplished people reading our columns. Gale
Grunwald, secretary/treasurer of Rosendale’s Century House Historical Society, sent us a Wikipedia posting about the hill that we had been looking at. It is called Joppenbergh Mountain. Then Steven Schimmrich, a professor of geology at Ulster Community College, sent us a very old New York Times article. Between the two of these sources we were able to put together the story.
Joppenbergh Mountain had, during the late 19th century, been the site of extensive dolomite mining. Numerous tunnels had been cut into the mountain (see our second photo) and the dolomite was used to make Rosendale Cement. That likely made the steep slopes of the mountain unstable. The cave-in was the result. It was associated with a series of landslides which began on Dec. 19, 1899. Thousands of tons of earth slid down the slopes of Joppenbergh. Fortunately, none of the miners were underground at the time and no one was hurt. But we are left wondering which came first. Did the cave-in trigger the landslides or was it the other way around. We are guessing the cave-in came first. And that is what we saw when we were hiking up the rail trail. With the help of our readers we had found an interesting geological explanation to our puzzle.
We hope you will go to the trestle and see all this. You might also visit the Century House Historical Society and its Widow Jane Mine. But, we also hope you will not attempt to climb into the old collapsed mine. That would be too risky. It’s been 117 years since the collapse; that is a little too late for its first fatality.