The Champlain Thrust was formed about 500 million years ago when two plates collided and overlapped. The upper plate is Dunham Dolostone; a carbonate rock plate thrust 35 - 50 miles over the Iberville Formation, which is composed of shale with calcite veins. Interestingly, the Cambrian Dunham Dolostone is older than Iberville Shale, which dates to the Ordovician. The fault extends from Canada to the Catskill Plateau, almost 200 miles. In the picture below, A is the Dunham Dolostone and B is the Iberville Shale, which has eroded away greatly.
If I knew more about geology, I'd go into more detail, but beyond what I've already written, I just don't really understand what I'm reading about! Something about slicklines...which I assume are grooves in the stone made by the movement of the plates against one another. They're supposed to be on the bottom face of the Dolostone. Here's a picture of the underside of the dolostone plate:
Are the lines extending from the upper right to lower left slicklines?
The shale was so eroded that it was almost powdery in some places, which made climbing around somewhat dangerous and very dirty. It was well worth it, though, to get up close to the rock and see the view of the lake from high up.
The geology of the area was only a piece of what made the hike so interesting, but you'll have to wait until the next post to see some of the flora and fauna.