LAST WEEK WE INTRODUCED you to the bedrock geology at High Falls in Philmont. That’s one of the locations preserved by the Columbia County Conservancy. One of us, Robert, will be leading a geology walk there on October 22 at 10 a.m. Last time we learned that the bedrock here dates back more than 443 million years to a time when Philmont and much of Columbia County lay beneath the waves of a very deep ocean, the Iapetus Sea. That bedrock was originally mud at the bottom of that ocean. This time our focus is on some peculiar features that can be seen in this, the canyon of Agawamuck Creek.
Take a look at our photo. That’s a boulder from the bedrock of High Falls. Notice the striking white stripes that cut through it. These are veins of quartz and they have a story to tell. They take us back several hundred million years to when there was volcanism going on beneath our region.
We don’t know exactly when this happened but it was likely during a mountain building event. There have been several episodes of mountain building hereabouts. The mountain building fractured the bedrock, and with time enormous masses of extremely hot water forced their way upwards along these faults. Hot waters can carry a lot of dissolved minerals, and when they cool those minerals can crystalize. In this case the mineral is white quartz. This is how the veins we see formed; they are called hydrothermal injections.
Contact the authors at . Read their blogs at thecatskillgeologist.com .