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CAPE COD GEOLOGY 



Gardiners clay, seen in the axis, is overlain by the Jacob sand, which is in places 

 contorted. About three feet of fine glacial gravel, which rests on the Gardiners 

 clay, forms the base of the Jacob sand in this anticline, so that the sand there 

 is not a transitional deposit. 



On the northern gently sloping limb of this anticline an excellent exposure 

 of the succession above the Jacob sand was seen in 1916. The overlying Herod 

 gravel included a bed of stony unstratified blue clay or till. Above this glacial 

 coarse material there is a bed of sand, which passes up into a bed of gravel 

 about 20 feet thick, upon which lies a typical boulder clay containing a lenticular 

 bed of gravel, the Montauk till. The surface cuts across this fold, which therefore 

 antedates the pre- Wisconsin surface of erosion recognized on the island. The 

 Montauk till also is folded down into the section just north of the Cretaceous 

 exposures in Clay Head, and is there underlain by the Herod gravel in such 

 manner as to raise the question whether the opinion that the Jameco gravel 

 lies upon the Cretaceous folds should not be replaced by the opinion that the 

 gravel lies at the Herod horizon. Certain details can be learned only after 

 the slumped part of the cliffs, at the most critical position for exhibiting structural 

 relations, has been cut back so as to afford fresh exposures. 



South of the Clay Head section folded beds of sand, sandy clay, blue clay, 

 and gravel were exposed in 1916, and south of a small valley that comes to the 

 coast at that place there was exposed a section of bouldery gravel in a sandy 

 and clayey matrix, overlain by about six feet of gray clay, the stratigraphic 

 relations of which are not perfectly clear but which may be an extension of one 

 of the beds seen farther north. 



The Mohegan Bluff section. — Excellent exposures of the older Pleistocene 

 from the Gardiners clay up through the Jacob sand into the Manhasset for- 

 mation, with its subdivisions of Herod gravel, Montauk till, and overlying Hemp- 

 stead gravel, make up Mohegan Bluff (Plate 30) at Southeast Point. The beds 

 have been thrown into rather gentle folds. No overturned folds such as are 

 seen at Gay Head in the older basal Pleistocene are commonly found in the 

 middle Pleistocene. 



VINEYARD INTERGLACIAL STAGE 



A cursory examination of the summit line of the cliffs of the island reveals 

 the fact that the beds of Montauk till and the associated beds of gravel (Herod 

 and Hempstead members) of the Manhasset formation, which form the highest 

 of the well-developed glacial deposits on the island, are everywhere truncated 



