These images were taken one morning while studying the glacial rock formations of Central Park, NY. I was looking for a certain type rock called Hartland formation, which is a type of bedrock. With few exceptions, the southern part of Central Park consists of rocks of the Hartland formation. North of roughly 80th Street, the metamorphic rocks are predominantly Manhattan Schist.
The striations that form on these rocks, were caused as debris is dragged across the glacier bed. Many of the exposures preserve glacially-polished surfaces, striations, and grooves carved from rocks embedded in the base of the ice sheet as it moved southward. Crenulation or Crenulation cleavage is a texture formed in metamorphic rocks such as phyllite, schist and some gneiss by two or more stress directions resulting in superimposed foliations (the lines you can see).
