Question

The tully limestone stands out as a ridge of rock between valleys developed on the Moscow and Geneseo formations. What might account for this landscape pattern?

Answer 1

The Tully limestone had undergone Moscow shale and then the Geneseo shale was laid on the top.

The erosion of shales is faster than the dolomite or the limestone which erode slowly and erosion occurs at a slower rate than shales. The formation of Geneseo is entirely shale. When the limestone is tilted on the edge, valley formation occurs on its either side due to the fast weathering of the shale. Two rivers on erosion cause the formation at distinct places of exposure of different shales and a ridge is left between them.

Answer 2

Shales weather in what are called a declining pattern. They erode more eagerly than limestone or dolomite which weather very slowly. If the limestone has been tilted on edge, a valley would form on either side of the limestone ridge since the shales would weather much more rapidly around it. Likewise if two rivers erode the formations at dissimilar positions of exposure of the different shales, the ridge will be left between them.