The Finger Lakes hold another great testimony of glaciation. The lakes occupy troughs. Troughs were first carved out by streams, then gauged by moving ice, and dammed in the South by the Valley Heads moraine. The region between Finger Lakes and Lake Ontario is a great example of drumlin fields. Drumlins occur when glaciers locally readvance and override a previously deposited ground moraine.
Drumlins are hills of glacial debris.
They are elongated in the direction of ice movement. The alignment of drumlins shows that the Lake Ontario basin served as a spreading center for ice moving outward in the region of Buffalo and Watertown.