The Sand-Plains of Truro, Wellfleet, and Eastham
Amadeus W. Grabau
Science, New Series, Vol. 5 (113): 334-335.
Feb. 26, 1897
posted June 2006
Science is published by American Association for the Advancement of Science.
THE SAND-PLAINS OF TRURO, WELLFLEET, AND EASTHAM.
(Abstract of a paper read before the Boston Society of Natural History, January 6, 1897.)
Lower Cape Cod exclusive of Provincetown, or that portion of the Cape comprised within the townships of Truro, Wellfleet, and Eastham, is made up of a succession of sand-plains, of the type so prevalent in eastern Massachusetts. The plains are numerous, nevertheless they can all be referred to three distinct series, differing from each other in elevation and direction of extent. The northernmost of these are the Truro Plains, with an average elevation of eighty feet above sea level. These stretch from High Head southward to about half a mile below North Truro village and eastward to Highland Light. Transverse depressions, with a general northeast and southwest trend, separate the individual plains of this series on the west, while depressions with a north and south or a northwest and southeast trend limit them on the east. The slopes bounding these depressions have all the appearance of old constructional slopes, no indications of subsequent erosion having been observed. As an exception to this, however, the slopes bordering Salt Meadow and Moon Pond Meadow on both sides of High Head should be mentioned, these having all the appearance of ancient erosion scarps. The most typical of the northeast and southwest depressions is the one occupied by the road leading from North Truro station to Highland Light. Here the northern slope has all the characters of a southward descending delta front of an ordinary sand-plain, while the slope to the south of the road resembles a northward descending ice-contact slope. This difference in angle of slope is well shown by the fact that the village of North Truro is built wholly upon the gentler delta (?) slope north of the road. This relation of slopes holds for all the northeast and southwest depressions, while in the north and south and in the northwest and southeast depressions the steeper ice-contact (?) slope is invariably on the west, and the gentler delta (?) slope on the east. Kettle holes are common.
The Wellfleet Plains stretch southward from Highland Light to Wellfleet village, with an average elevation of 140 feet above sea level. Highland Light plain is a typical example. For the main part, a depression
exists between the Truro and Wellfleet plains, the latter presenting steep ice-contact (?) slopes towards the northwest.
South of North Truro village, however, the lower plain joins on directly to the higher. Kettle holes are common. Standing upon the high ground a mile north of Truro station and looking east, the whole series of plains seems to descend by a gentle delta (?) slope toward the west, leaving a deep and irregular depression occupied by the Provincetown turnpike. In the vicinity of Small's Hill a number of profound northeast and southwest depressions dissect the plain. These are occupied by the roads leading to the east shore. The slopes on both sides of these depressions are steep, and although they probably have been modified by wind the indications are that they are due to former lobes of ice dissecting the growing delta. Pamet River completely divides this series of plains, the southern portion being much more irregular and hummocky than the northern and also containing a number of kettle ponds.
The Eastham Plains are typically developed about North Eastham village. This series may be better regarded as one continuous plain uniform along the eastern shore from Wellfleet to the ' Three Lights,' where the elevation is about seventy-five feet above the sea, and the whole plain gently sloping westward. The northern half of this large plain is dissected by discontinuous east and west, and northwest and southeast depressions, with steep ice-contact (?) slopes on the south and lobate delta (?) slopes on the north. In the southern half of the plain the depressions have a north and south trend, with the steep ice-contact (?) slopes on the west and the delta (?) slopes on the east. South of Eastham Centre the plain joins on to the moraine. This plain was probably formed while the Truro Plains were accumulating and after the Wellfleet Plains had been formed. The latter seem to have been built by streams from the north and east. The Truro plains were built by streams from the northwest and northeast, while the Eastham Plain was being built by streams from the east. The terminology is applied to the slopes with some reservation, as almost the only criterion by which to judge of their character is the relative steepness and the general outline. Cuttings are very rare, and hence the relative coarseness of the material, and its disposition within the plains cannot be ascertained. The sections along the shore exhibit horizontal stratification where not covered by talus.
It seems difficult to believe that these plains have not accumulated in static water at the front of the much-dissected ice sheet. Submarine accumulation seems improbable, as erosion scarps would have been formed on the higher plains during the formation of the lower. On the other hand, if a body of fresh water was held up against the moraine, in an embayment in the ice front, it would be necessary to suppose that the ice held on to the moraine from Barnstable eastward, and that a residuary plug of ice filled the valley of Buzzard's Bay. This latter necessity is probably the most serious defect of the glacial lake theory.
Amadeus W. Grabau.