20 miles across. Behind the dam, the lake slowly filled with layer upon layer of silt and clay. In the winter months, the lake froze over, reducing circulation of lake water by shielding it from the stirring action of wind and waves. The calmer winter water deposited clays even finer than the silts of summer, leading to an annual cycle of sedimentation corresponding to the seasons. The result was a banded type of stratified drift called varves. Similar to tree rings, each varve records the passage of one year.

Streams flowing into Glacial Lake Hitchcock (and other smaller glacial lakes) carried heavy loads of sediment because of the inability of the sparse tundra vegetation of the time to hold onto the many loose deposits of drift. The streams poured sediment into the lake and formed miniature versions of the Mississippi Delta. These fans of sandy sediment are another type of stratified drift known as glacial deltas. (Bradley Airport stretches across just such a delta built into Glacial Lake Hitchcock.) After 4000 to 5000 years, the unstable dam at Rocky Hill collapsed, draining the lake forever. But the varves, glacial deltas, and other sediments of the lake still remain, creating the flat terrain and fertile soils of this region - a rich gift of glaciation.

Because Lake Hitchcock formed in the later part of the retreat of the ice sheet, its sediments were laid down on top of the Valley's till. This blanket of fine-grained lake sediments protects farmers in the Lake Hitchcock region from even the mild stoniness of Valley till. Till lies at the surface only in those areas that reached above the height of the lake's waters, mainly along the margins of the Valley. Occasionally, a large lump of till pokes out through the lake sediments in the form of distinctively shaped hills known as drumlins. These till hills typically have a streamlined, egg-shape that is elongate and rounded. The distinctive shape of drumlins makes them easy to recognize. A few examples in the Central Valley include the Blue Hills of Bloomfield and Hartford and Indian Hill in Middletown. A good example of a drumlin in the Uplands is Horse Barn Hill, the hill cultivated by the University of Connecticut's agriculture department, just east of Route 195 at the edge of the Storrs campus.

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