All your life you have been driving past rock outcroppings. How many times, if ever, have you taken any real notice of them? Well, why should you; they are just rocks, aren’t they? Perhaps, if you have been reading our columns, this has changed; maybe you have been taking notice. We hope so. It isn’t just being able to identify rock types; sometimes there are things that can be pondered, ideas that deserve real thought, even deep thought.
We pondered these notions recently when we passed an outcrop along Rte. 23 where it crosses over the Jefferson Heights Road (Rte. 23A) just west of Catskill. Take a look at our photo. That’s a pretty dull looking pile of rocks, isn’t it. It’s just a gray sequence of stratified rock. What is it that geologists find so interesting in such things? Well – plenty of things. A geologist would first ask what kind of rock is it. Any experienced geologist would immediatel recognize it as a limestone. That would conjure up all sorts of images of the sparkling blue waters of a very ancient shallow tropical sea. This one is the Helderberg Limestone, named for the Helderberg Mountains where these rocks are so common. Once, about 400 million years ago, there was a tropical sea – right there. You can’t help but look around and envision those images.
But there is more, so much more. Those limestone strata are deformed; they are inclined to the right. They were actually physically tilted; we recognize that because we know that strata of all stratified sedimentary rock must have been originally deposited as horizontal sheets. Gravity spreads those sediments out into those sheets. If they are no longer horizontal, then something must have happened to them.
And that something was mountain building. This location, once a shallow sea, experienced the effects of plate tectonics. Something big, quite likely a sizable piece of Europe, collided with North America. Now, that’s a thought, isn’t it? We geologists have gotten so used to swinging whole continents around – like baseball bats. We pick up one continent and then swing it until it slams it into another. The result, big surprise, is a compression of the rocks on the receiving end. One reaction to this is for those rocks to be folded, and that folding often produces just the sort of tilting that we see here.
These things are so simple to explain, but that gets us back to where we started. It’s so easy to just pass by a rock outcropping and take no notice of such things. Again, they are only rocks. But, then there is more; you can’t help but ponder who was it who first really noticed such things. And, who was it who first asked questions about them? And, most importantly, who first started to answer such questions? You must understand that these simple notions were once incredible feats of original thinking – of true intelligence. Fortunately, we do know who it was. History tells us that. Let’s pursue this next time.
Contact the authors at randjtitus@prodigy.net. Join their facebook page “The Catskill Geologist.” Read their blogs at “thecatskillgeologist.com.”
0 comments:
Post a Comment