Deltas were built wherever streams from the highlands entered the valley, and they mark the ancient level of the lake. Strangely, their elevation drops from 315 feet at Montague to 300 feet at Amherst, and is only 268 feet at South Hadley. The changing elevation shows either that the lake surface sloped southward—and indeed this would be unique—or that the shoreline was raised in the north and that the lake drained southward. The latter surmise is plainly the more plausible. Most deltas on the east side of the valley are pitted by numerous conical depressions. In a depression on a delta plain near Montague, an excavation, made to obtain road fill, disclosed a mass of disordered gravel which must originally have been deposited in the horizontal top-set beds of the delta, but which now lies in the bottom of a depression mingled with the fine sand of the underlying fore-set beds. The top-set beds seem to have been supported for some time and then collapsed as if the underpinnings were removed. The crudely circular or elliptical outlines of the depressions suggest that stray icebergs drifted upon the delta slopes, where they were anchored or buried by the sandy outwash. The buried ice-cakes survived until the lake was drained, and the baselevel of the streams was lowered, for the depressions have no outwash within them. They collapsed soon after the lake vanished, because water soaking through the delta sands melted the ice, much as it thaws the ground for dredging in the Yukon. Even today this gravelly ground, particularly the beach of the ancient lake, is well drained, and it forms the best land for the apple orchards of the valley. _Glaciers Came_ The delta deposits and the clays form a thin veneer over a bouldery soil that comes to light along the delta-top margins and in gulches cut down through the gravel and sand. Some of the boulders are huge, attaining diameters of twenty feet; and all are strangers to their present resting places. Some are set upon a bare rock floor, scratched as though by sandpaper, and they teeter to the weight of a child; most are embedded in soil. These “erratics” seem to have been left like unwanted objects, picked up and carried for a time, and then dropped when the bearer wearied of their weight. The scratches on the rock floor are parallel grooves, all of which trend southward. They are unmistakable tracks left by glaciers, and the boulders are like the stones perched on glacial ice for a ride to the terminal moraine.