62 



CAPE COD GEOLOGY 



area in the second or Falmouth substage of the Wisconsin ice is the earlier 

 melting of the ice on the west than on the east. The streams of water that built 

 the high sand plains between ice block holes in the western part of the interlobate 

 moraine, about Plymouth, poured southwestward from the lobe of ice lying over 

 Cape Cod Bay, and, as Grabau * pointed out, the outwash plain at Eastham, 

 on the arm of Cape Cod in that interlobate axis, was also traversed by streams 

 running toward Cape Cod Bay, coming from ice lying east of the site of Cape 

 Cod. It would thus appear that the Wisconsin ice sheet thinned and melted 

 away over the present mainland before it melted over the Bay of Maine in the 

 latitude of Cape Cod. 



The moraines of this substage form the surface features of the Elizabeth 

 Islands, but apparently not the mass of drift that stands above sea level in those 

 islands. On Naushon and other islands large boulders are grouped in lines showing 

 the faltering retreat of the ice front across these broad, low Pleistocene ridges. 

 Almost everywhere in the islands a bed of yellow sand underlies the surface 

 moraines. Conjectures as to its stratigraphic position are given in the text deal- 

 ing with these islands (Pt. 3, Chap. 2). Back of the main Falmouth moraine there 

 are numerous retreatal moraines, only a few of which lie within the area covered 

 by this report. 



Interlobate Moraines 



Enormous piles of gravelly and sandy drift lie on the west shore of Cape Cod 

 Bay, in the Plymouth woods, extending as far north as Kingston, Mass. These 

 deposits are here called the Plymouth interlobate moraine. This moraine is a rude 

 ridge of rather bouldery drift or till, sections of which disclose older Pleistocene 

 deposits, including a blue clay of either Montauk or Gardiners age. Most of its 

 sections in the interior show stratified beds of gravel. The highest mass of this 

 moraine forms Manomet Hill, which has an elevation of more than 380 feet above 

 sea level. A cut made in the northern part of the crest of this hill when the roads 

 of the state were being reduced to standard grades showed a coating of gravelly 

 till, some 12 feet thick, overlying waterlaid gravel, confirming the opinion that 

 most of the glacial drift in this moraine is stratified. This eastern, more decidedly 

 morainal part of the deposit is separated from the area of plains and ice block 

 holes on the west by a line of lakes that occupy ice block holes. These lakes, 

 which are the largest in the district here considered, include Billingston Sea, 

 famous in the annals of the Pilgrim Fathers, one of whom is commemorated 



1 Grabau, A. W., The sand plains of Truro, Wellfleet, and Eastham, Science, new ser., 5, pp. 334-335, 

 Fehruarv 2fi 1897. For discussion of this paper, see same volume, p. 361. 



