Station B

Not Just a Rock  (U3.2)

The embedded rock you see on the trail is a metamorphosed sandstone.  It is part of the underlying bedrock and illustrates the geological history of the park.  This rock was formed during the Pennsylvanian Period which occurred from 323.2 million to 298.9 million years ago.

Glacial striations (arrows)

The long parallel scratches called glacial striations on the gray sandstone were formed during the Pleistocene glaciation which spanned from 2.6 million to 11,700 years ago. So how were the striations etched into the rock?

Answer >

Picture really hard bits of rocks being frozen onto the bottom of a glacier that might have been as thick as two thousand feet.  They were then dragged across the surface of the softer sandstone beneath as the glacier advanced or retreated. 

Glacial striations in various stages of preservation can be seen on other rocks along the Upland Trail at U0.8 and U4.5.  Weathering has caused some of the striations to be quite faint, but they are noticeably all aligned in the same compass direction.