Site 6: The Upstream Cracks

This is a quick little site to wrap everything up. Most of what is discussed here in a comparison of these cracks to the cracks at site two. Take a look a look at the posting for site two to refresh you memory. These cracks are wider, appear deeper, and the rock itself is much more rounded. The acid test revealed that this rock is limestone. The same test performed at site 2 yielded dolostone. Because limestone is more susceptible to chemical weathering by the acidic runoff, the rocks here show greater weathering, thus the larger cracks.

Site 3: Boulder and Tree

At this site we discuss how limestone, a rock very resistant to physical weathering, is very easily weathered by chemical means. Acids from naturally occurring and man-made acid rain, as well as natural acids from the decomposition of leaf litter contributed to the solution channels we see across the top of this boulder.














Along the the side, there are several chert nodules that show differential weathering. Chert is a variety of quartz which is very resistant to physical and chemical weathering. Since it weathers more slowly, it sticks out.








At the very bottom of this boulder, we find a very interesting fossil of a cephalopod. This was a creature that looked much like a squid, but had a conical external shell. Cephalopods lived in warm, shallow tropical oceans. How is it that this area of NYS was once warm shallow tropical ocean? Plate Tectonics!



Across the stream we investigate a tree that appears to be growing out of the side of the cliff. Closer inspection reveals flattened roots that were shaped as they grew in cracks of the bedrock. As the roots grew, the wedged the rock apart, it was then eroded away by the stream.

Site 2: Swirls and Joint Cracks

Site 2 is really fun. Crayons and everything! At site 2 we investigate the very strange swirls in the surface of the rock. These are trace fossils of a sea floor dwelling worm called zoophycus that lived a long long time ago (Silurian) when this area was the bottom of a tropical ocean. This is not a fossil of the worm itself but of marks it left in the sediment.

The second item investigated at this site are the amazingly straight, amazingly parallel cracks in the bedrock. These are called joint cracks. They formed when the glaciers melted removing a great deal of weight from the surface of Earth. The continental ice sheets weighed so much they had pushed the crust down into the mantle. As the crust rebounded the cracks fromed from pressure unloading.