Preliminary Results of Recent Deep Drilling on Cape Cod, Massachusetts

Abstract

In 1961 a 1000-foot drill hole near Harwich on Cape Cod, Massachusetts, penetrated 435 feet of Pleistocene deposits above 50 to 60 feet of crystalline limestone and phyllitic schist, and more than 500 feet of phyllitic schist with abundant quartz veins. Similar rock is known in the Pennsylvanian and Precambrian (?) sections of Massachusetts and Rhode Island. Material of Eocene age was found in earlier drilling near Provincetown, but none was identified from this hole.

Geologic map of the Harwich quadrangle, Barnstable County, Cape Cod, Massachusetts

“…Therefore the drift on Cape Cod is believed to be about 14,000 to 15,000 years old. The oldest deposits in the quadrangle are the till and silt identified in the boreholes and seismic surveys (Koteff and Cotton, 1962;Oldale and Tuttle, 1965). The till is believed to be a basal till deposited by the last ice.…”

“…Silty clay in the fluvial deposits was laid down in small ponds caused by the partial m e 1 tin g of buried ice blocks. The thick silt layer identified in the borehole in Harwich (Koteff and Cotton, 1962) suggests that the Harwich outwash plain may be a proglacial delta deposited in a lake that occupied Nantucket Sound. If so, the outwash exposed above sea level would be delta topset beds graded to the level of the lake.…”

“…Glacial lake and lake bottom deposits occur north of the Sandwich moraine and Harwich outwash plain deposits, and are the youngest glacial deposits in the quadrangle. Borehole data from the quadrangle (Koteff and Cotton, 1962) show that the mapped deposits are at least 160 feet thick and overlie a coarse to clayey silt 153 feet thick that in turn is underlain by compact till 116 feet thick that rests on crystalline basement. There are 1 no major till layers at the base of the mapped deposits or interbedded with the silt, therefore the silt and overlying sandy deposits are believed to have been laid down during a single glaciation.…”