Ice contact deposits of the Alaskan Malaspina Glacier. Till, boulders, and sand and gravel are underlain by the irregular surface of melting ice. The rock debris deposited by glaciers is called drift. It overlies bedrock that is similar to the hard rock that crops out throughout the rest of New England. On Cape Cod, the bedrock is buried by glacial deposits ranging from more than 200 to more than 600 feet thick.
Drift consists of very fine to very coarse rock debris.
If unstratified and unsorted, it is called glacial till. Till is deposited directly by ice and is unsorted because ice cannot separate rock fragments of different sizes. Thus, it is a mixture of all sizes of rock debris ranging from clay-sized particles to very large boulders. Stratified drift, on the other hand, is deposited by water which can separate the different sizes of rock fragments. The rock fragments are deposited in layers called strata.