98 



CAPE COD GEOLOGY 



Sankaty Head, on which it spread a thin veneer of drift. The surface over which 

 this ice sheet advanced was produced by the erosion of the folded bed of till and 

 the bed of shell-bearing sand, a bed that had evidently been already deformed 

 and folded by an ice advance antedating the deposition of the Montauk till. 

 We are thus led to place the bed of till that overlies the Sankaty shell-bearing 

 deposits below the horizon of the Gardiners clay and at the horizon of the Jameco 

 formation, which has a till phase (Moshup till member) on No Mans Land 

 and at Nashaquitsa cliffs, or to place the bed of till overlying the Sankaty sand 

 at the horizon of the stony blue clay in the Gay Head section, which in this 

 report is referred to the Mannetto formation, a conclusion similar to that indi- 

 cated by the facts first presented. I am, therefore, inclined to place the Sankaty 

 shell-bearing beds very low down in the Pleistocene series, above the Dukes 

 boulder bed and under the Jameco and its Moshup till member, at the horizon 

 of the beds of glacial sand and gravel found at the east end of Nashaquitsa cliffs 

 (the Weyquosque formation of this report), or in like relation to the Sankaty 

 beds of my earlier paper. 



If this argument is valid, no Pliocene deposits have yet been found on 

 Nantucket. But as the delimitation of Pliocene and Pleistocene deposits has 

 been determined by somewhat arbitrary and very different standards and criteria 

 it may be possible that here on the seacoast the glacial and interglacial deposits 

 may have become interlocked with coastwise marine deposits that extend south- 

 ward beyond the glacial limits and that have been regarded as parts of the Plio- 

 cene series. 



FOSSIL SHELLS UNDER THE INTERIOR OF THE ISLAND 



Several references to fossil shells encountered in digging wells and making 

 excavations are found in the literature concerning Nantucket. Most of the 

 wells in New England were dug long ago and no records were made of the beds 

 penetrated. 



In 1882 E. K. Godfrey l published a note by Mrs. Anne Mitchell Macy on 

 "The botany, conchology, and geology of Nantucket," in which she states that 

 shells like those seen in the bluffs at Sankaty Head had been found far from the 

 bluffs. Mr. Godfrey also reproduces a letter written by Zaccheus Macy to the 

 Massachusetts Historical Society, dated Nantucket, "ye 2d ye 10 mo., 1792,", 

 in which he says he found shells in his well at depths nearly 40 feet below the 

 surface. 



Dr. J. Howard Wilson states that in boring for a well many years ago on the 



* Godfrey, E. K., The island of Nantucket, Boston, 1882, pp. 32-33. 



