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A drumlin field is a cluster of dozens to hundreds of similarly shaped, sized and oriented drumlin hills. Drumlins are one type of landform that indicate continental ice sheet glaciation. The total depth of glacial deposits may be hundreds of feet deep.
Lake Ontario example
The shaded relief map depicts a large drumlin field that exists in New York between the south shore of Lake Ontario and Cayuga Lake, which is just south of Montezuma Marsh. The old Cayuga valley north of Montezuma Marsh is almost entirely buried under the drumlin field. Possibly the bay at Fair Haven is a remnant of the old valley.
This drumlin field is unique, in that it was greatly modified after it formed. Apparently, as the glacier retreated, it blocked the Lake Ontario outlet through the present St. Lawrence River for a long period, holding the lake at a higher level. A clearly marked shoreline resulted as shown by the light blue line. Drumlins north of that line were islands in the old, larger lake. Near the shore, wave action eroded and entirely removed the drumlins. Farther north, where the water was deeper, the waves eroded the top from each drumlin leaving them with an unusual flat top, instead of the normal elongated dome shape.
There is evidence that the glacier did not advance in a straight line, but rather in the fashion of a tongue or lobe of ice. In the lower right of this image, the orientation of the drumlins show that the ice was moving east of south. As one looks at drumlins farther west, in the Rochester, New York area, the drumlins show a turn to the west of south, and as one approaches the Niagara River, the drumlins align almost westward.
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