GLACIAL DRIFT. 3OI 



ties in the geological report of Massachusetts, and of Long Island in that of New York, 

 seemed to indicate that these areas would show lenticular hills ; but no accumulations 

 like those which we have been describing under this name were seen. 



The greater part of southern Plymouth county was found to be covered with modi- 

 fied drift. Much of this is spread in level plains, which in Middleborough have many 

 shallow depressions that are occupied by swamps. In the west part of Plymouth the 

 only hollows which break the plains are of small area with steep sides, containing 

 ponds. These are so numerous that this township is said to have a pond for each day 

 in the year. About Plymouth village the modified drift forms kame-like hillocks and 

 small plains, which are separated by very irregular hollows and valleys. The tops of 

 these deposits have a nearly uniform height which varies from 100 to 125 feet above 

 the sea. 



In the east part of Plymouth a massive ridge, known as Manomet or Rocky hill, ex- 

 tends three or four miles from north to south, having a continuous height 300 to 400 

 feet above the sea. Abundant angular boulders of all sizes up to twenty feet in diam- 

 eter strew its surface, wliich seems to have no ledges, but to consist entirely of the 

 very coarse glacial drift that we have called upper till. At the north end of this range 

 the sea has undermined its base, forming a steep slope sixty feet in height. A section 

 here showed twenty feet of upper till, yellowish, with abundant large and small boul- 

 ders, nearly all of them angular, underlain by lower till, dark bluish gray, with small 

 glaciated stones, exposed for twenty feet vertically but concealed below. The bed 

 of boulders which forms the shore at this point came mostly from the upper stratum ; 

 their sharp corners and edges have since been worn away by the waves. This ridge 

 is bordered on both sides by kame-like or nearly level areas of modified drift. 



Southward, a broken range of lower hills, composed of the same coarse till, continues 

 through Plymouth, Sandwich, and Falmouth. Thence it bends to the south-west, 

 forming the chain of the Elizabeth islands. The highest elevations of this series of 

 hills in Sandwich are about 300 feet, and in Falmouth and upon Nauslion and the 

 islands farther west, nearly 200 feet above the sea. Its length, from Manomet hill to 

 the end of the Elizabeth islands, is forty-five miles. 



Railroad cuttings thirty feet deep in these deposits, one mile north of Falmouth 

 village and Wood's Hole, show only the upper till. All of Naushon island consists of 

 the same material upon the surface, namely, mingled boulders, gravel, and sand, wholly 

 unstratified. The boulders are often so abundant as to cover all the ground, and are 

 of all sizes up to ten, or even twenty or thirty, feet in diameter. They are almost inva- 

 riably angular, except as they have been rounded by exposure to the weather, none of 

 them, so far as observed, being glaciated or water-worn. Cliffs forty or fifty feet high, 

 which are being undermined by the sea south-west from Tarpaulin cove, appear to be 

 composed entirely of this coarse upper till ; but on the north-east end of the island a 

 well sixty-seven feet deep passed through this deposit, and its last twenty-two feet 

 were in very hard lower till, dark gray in color, with glaciated pebbles. 



The contour of this island, as also of many localities throughout the whole series of 

 VOL. III. 39 



