Figure 4. Bedrock surfaces not only look different with varying illumination, but show certain details more clearly when they are wet. This photo shows a ledge in Warren that has been smoothed by glacial abrasion. The dry (light colored) part of the outcrop shows compositional layering within the metamorphic rock, but glacial markings are not obvious. The darker part of the rock surface is wet, and light reflection from this area reveals two sets of glacial striations of differing age. The younger and dominant set (parallel to red pencil) indicates ice flow to the east-southeast (115°), while shallow swales preserve older striations produced by regional ice flow to the south-southeast (154°; marked by blue pen).
Last updated on July 9, 2012