Drumlins are till deposits formed beneath the glacier.
They are shaped like the bowl of a teaspoon turned upside down. The
steep blunt end is on the side from which the glacier originated; the gentler
slope trails off in the direction the glacier was moving. Drumlins
usually occur in groups. Eastern Wisconsin is particularly noted
for its drumlin fields. The photograph below is from a drumlin field
at the south end of Lake Winnebago.
Although the vegetation somewhat obscures the hilltop,
it's general outline is discernible.