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. Gravel and sand are sorted and stratified by meltwater flowing in streams draining the glacier. Most of the drift has been fashioned into either moraines or outwash plains. Both features mark positions of the ice front.
Moraines are ridges of drift formed by moving ice.
Most moraines are formed when the ice front remains more or less in the same place because advance of the glacier is balanced by melting along the ice front. When the debris falls free of the ice, it accumulates along the ice front much like material at the end of a conveyor belt. However, the Buzzards Bay and Sandwich moraines were formed in a different way. They were formed when an advancing ice front overrode sediments it had previously deposited or sediments that were older than the last glaciation. The advancing ice thrust sheets of drift upward and forward to form a large ridge beyond the ice front.