270 



CAPE COD GEOLOGY 



gravel and sand that reach a height of about 250 feet above sea level where the 

 State road crosses the northern spur of the hill. The approach of the summits 

 of the pre-Wisconsin deposits to a height of 300 feet suggests a former base level 

 at that height. 



Road cuts on the northern slope of Bourne's Hill expose stratified beds of 

 gravel, sand, and clay under a thin veneer of till, generally less than 4 feet thick. 

 The mass of the hill is probably made up of outwash from the ice front. 



From Bourne's Hill westward and southwestward through the town of 

 Bourne the moraine forms the iceward border of a great outwash plain that is 

 backed by a high ice-contact slope having a morainal topography and a surficial 

 cover of thousands of granitic boulders, many of them gathered in huddles. 

 The Manomet Creek depression, which is followed by the Cape Cod Canal, 

 skirts this ice-contact border as a deep fosse separating the Falmouth moraine 

 at the interlobate angle from the huge mass of drift on the north, in the Plymouth 

 interlobate moraine. From Pine Hill, in Bourne (altitude about 260 feet) the 

 morainal mounds slope southwestward and the plain on the east slopes south- 

 ward, toward the Sound, at a steeper grade. 



In this higher part of the Falmouth moraine the deeper cuts show that 

 stratified sand is the chief constituent of its mass. The till varies greatly in 

 thickness from place to place. Its greatest thickness is exposed in borrow pits 

 20 or 30 feet deep, but the till and coarse waterworn cobbly drift must form a 

 very small part of the total mass deposited by outpouring streams at the front 

 of the ice. Here as in areas farther east, in Brewster and Barnstable, masses of 

 the Nantucket ice sheet remained while the great fan of outwash sand was 

 deposited. Some of this sand was laid down in front of the ice, particularly in 

 Falmouth, where Long Pond, now the town reservoir, extends from the plain 

 halfway through the frontal moraine. 



Many small sections exposed along the ice-contact face of this moraine in- 

 dicate that the ice kept pushing on the sand deposited immediately at its front, 

 advancing upon it one to three miles, as is well shown at the interlobate angle 

 southeast of the village of Bourne. The morainal ridge at Woods Hole, as indi- 

 cated by the mode of development of the moraine farther northeast, must also 

 be only superficially composed of bouldery till. Like other parts of the Falmouth 

 moraine it was doubtless laid down from ice masses at the Nantucket substage. 

 At many places these ice masses appear to have served as barriers behind which 

 outwash streams built up high-lying masses of sand and gravel. (Fig. 21). 



