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CAPE COD GEOLOGY 



lakelets are seen at the east and west ends of the island, either in the glacial 

 drift or behind barrier beaches thrown up by the waves. 



The island is covered with bouldery drift of the Wisconsin stage, in which 

 there are numerous kettle holes, 30 to 50 feet in diameter, which contain lakelets 

 or swamps. The north coast is covered with drift. On the steeper and more 

 exposed south coast, Mr. Gilbert Hart, my assistant, observed a cut in the 

 bank showing 4 to 8 feet of till covered by a bed of sand 4 feet thick, under 

 which 3 feet of clay was exposed down to the base of the bluff. 



At the east end of the island, between the two small ponds shown on the 

 map, clay has been dug. The till at this point is little more than a coating of 

 scattered boulders embedded in a sandy soil or subsoil one or two feet thick. 

 Well defined waterlaid sand, 3 to 4 feet thick, underlies this till and is underlain 

 by the clay. This clay is probably underlain by pre-Wisconsin drift, as is shown 

 more clearly on Nashawena. 



A small islet of glacial drift off the southeast end of the island supports 

 bars that tie it to the main island and enclose a small marsh. A barrier beach 

 thrown up on the north coast encloses another small marsh. The beaches are 

 largely bouldery. 



NASHAWENA ISLAND 



The island of Nashawena, the second largest in the group, is about 21 miles 

 long and from three-fourths of a mile to lh miles wide. Its glacial features — 

 its ridges of older Pleistocene sand, its long hollows, and its kettle holes — are 

 essentially the same as those of Naushon. Most of the broader ridges are in the 

 southwestern part of the island, where at three places they rise to heights 

 exceeding 120 feet. A deep depression lies in the western part of the island. Here 

 the steep slopes on the east, south and west sides of a small glacial lakelet show 

 that it was formed by an ice block or a tongue of the ice sheet. Two depressions 

 on the south side, which extend southeastward down to sea level appear to 

 mark the path of a glacial stream. 



The north coast of the island is covered with till or, where the sea has formed 

 cliffs, with a talus of bouldery drift. At several places on the south coast, where 

 steep bluffs show that the sea has cut back the land, beds of clay that rise 

 several feet above sea level may be seen. Most of the clay on the weathered 

 surface is whitish, but that within the bed is blue or brown where it is oxidized, 

 resembling the clay exposed on Cuttyhunk. The bed appears to be a phase of 

 the Gardiners clay, which is much better exposed on Marthas Vineyard, Block 



