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 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.