When the Croton Branch was beheaded by drift choking up its valley
west of Andrew Pond, the ponded waters rose to a height of from 20 to
30 feet and then overflowed the basin on the side toward Danbury. The
outlet was established across the old divide, and as the gorge by
which the water escaped was cut down, the level of the ponded waters
was lowered. At the same time, also, the lake was filled by debris
washed into it from the surrounding slopes. Thus the present flat
plain was formed and the old valley floor, a local peneplain developed
on the limestone, was hidden.