188 



CAPE COD GEOLOGY 



the Wisconsin ice sheet was so weak that the beds which it overrode were practi- 

 cally not deformed by it. The only places where any distortion could possibly 

 be made out would be those where the ice front encountered a cliff or other 

 abrupt topographic feature. Being a waterlaid deposit, the gravel shows bedding 

 wherever it is exposed. It contains no beds of till that might have been formed 

 by re-advances of the ice, such as are found in parts of Long Island. Some 

 thin layers of clay, however, are found in beds of gravel that probably belong 

 to the Hempstead. 



Conditions during deposition. — The Hempstead gravel was laid down when 

 the ice was retreating, a fact that suggests a somewhat milder climate than 

 that which prevailed during the Montauk stage, although the retreat may have 

 been due solely to a slackening in the speed of the advancing ice. At any rate, 

 the time was one of melting; water from the ice was washing materials out 

 of it and depositing them. Vegetation was probably very scarce, so that the 

 deposits were subject to rapid erosion. 



Distribution and outcrops. — The Hempstead gravel is found only along the 

 northwest and northeast shores of Martha's Vineyard and in the inland areas 

 that border these shores. Beds of gravel of this age may lie below the outwash 

 gravel in the great plain area, but they have not been recognized ; in fact, it would 

 be impossible to distinguish them from the overlying outwash unless an uncon- 

 formity could be recognized between the two. 



Northeast of Menemsha Creek, in the cliffs along the shore, some beds of 

 sandy gravel that are supposed to be Hempstead are exposed above the Mon- 

 tauk till. Farther northeast no beds of gravel that can be placed at this horizon 

 are seen until the section northeast of Roaring Brook is reached. Near the 

 northeast end of this section there is a small patch of sandy gravel, which over- 

 lies the Montauk till conformably and is in turn overlain by the Wisconsin till. 

 The largest exposure of probable Hempstead gravel is at Cape Higgon. Here 

 some beds of sandy gravel, exposed to a thickness of 40 feet, seem to overlie 

 the Montauk. This gravel is exposed for about 500 feet along the cliff. Another 

 exposure occurs a little more than a third of the way from this point to Cedar 

 Tree Neck, where gravelly sand and laminated fine sand and clay overlie the 

 Montauk till. In the cliff just south of Cedar Tree Neck there is an obscure 

 section showing bedded sand, probably of Hempstead age, overlying the Mon- 

 tauk till. The sandy gravel northeast of Cedar Tree Neck is also probably Hemp- 

 stead. In the Norton Point section some of the uppermost beds of gravel are 

 perhaps Hempstead, although the Montauk till is but poorly exposed. 



