Photo 3. Conglomerate in the lower member (Member A) of the Rangeley Formation. The cobble-sized clast of plutonic rock (P) is well-rounded. Plutonic rocks are a class of igneous rocks that form underground, and have large, interlocking mineral grains. This clast is probably granodiorite or tonalite rather than granite. It is common for certain rock types to form sedimentary clasts of a particular shape, as this round clast represents. The rock to the right of the line is pebble conglomerate, while the rock to the left is cobble conglomerate. These were different layers that formed in sequence, one on top of another, even though the layers are now nearly vertical. (Maine Geological Survey photo)

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Last updated on January 4, 2013

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