The upland continues southward through the Berkshire and Litchfield Hills, descending in a series of almost imperceptible steps towards Long Island Sound and the Atlantic. A few miles south of Litchfield, Connecticut, its low angle of declivity increases abruptly, and the more steeply inclined surface passes beneath the waters of Long Island Sound. The sudden change in dip suggests that two erosional planes are present and that each was formed under somewhat different circumstances and in different periods of geologic time. The soundness of this surmise can be demonstrated in Long Island where sediments laid in a Cretaceous sea rest upon the older and more sharply inclined erosional plane and rise approximately to the level of the New England upland. The deposits form a wedge between the two planes, and their Cretaceous age supplies a series of dates that would otherwise be difficult to establish in New England’s geological history. Erosion fashioned the New England upland in the early and middle epochs of the Tertiary period, immediately following the deposition of sediments in the Cretaceous sea. And the southward sloping plane upon which those sediments rest records an even earlier episode of denudation—an episode lost in the shuffle of later events in Massachusetts but preserved in fragmentary form in Connecticut, thanks to the protection afforded by the sedimentary cover. Had we lived in central New England when erosion of the upland and of the younger straths was in progress, we would have noted that the valley forms were well defined in the headwaters and lower reaches of the streams, which made their way through a country of light-colored or gray clayey soil. In the middle reaches the valley boundaries were blurred and indistinct, and the country through which they flowed was surfaced by red and sandy soil. The middle region is now the lowland, but even then it formed a depression athwart the topographic and hydrographic features of the country; and its distinctive red soil resembled alluvial wash or fill in a long basin. Its low relief would have been as impressive in early Tertiary time as its higher relief is today, for then it had little topographic competition anywhere between the present sites of New Haven, Connecticut, and Northfield, Massachusetts.