246 Geology of Martha^ s Vineyard. 



Clay Formation.* It cannot, however, be referred to any 

 other European formation, of which I have seen a descrip- 

 tion. It is coloured, on the accompaning map, only as a 

 belt along the coast, in those parts vi^here I have noticed it 

 to be more or less distinctly laid bare; although, as before 

 observed, it probably constitutes the basis of all the dilu- 

 vial part of the island. But the diluvial is so remarkable, 

 that it seemed to deserve a place. Probably, also, the 

 Plastic Clay underlies the diluvium of the Elizabeth Islands : 

 although the clay beds are not so distinct in the cliffs, and 

 are in general, hid by the sand. And from all I can learn 

 of Natucket, this island is, with little doubt, referable to the 

 same formation: if so, where, but to the same place in 

 the geological scale, shall we refer the sands of Cape 

 Cod 1 unless, indeed, they may belong to a formation still 

 more recent. Long Island, in those places where I have 

 seen it, is unquestionably very similar in its geological 

 structureto Martha's Vineyard ; and probably belongs to the 

 same era. I take it for granted, that the vast region along 

 the sea coast in the middle and southern states, marked on 

 Maclure's map as alluvial, can no longer be considered 

 such, in the modern sense of that term. He describes a 

 part of it, at least, as consisting of sandstone and limestone, 

 and regular beds of sand, gravel and clay; and some of this 

 gravel is cemented by oxide of iron : and, therefore, it can-t 

 not be alluvial ; but agrees with the European strata above 

 the chalk. If we take his map, and prolong the line, or 

 rather curve, that separates the alluvial tract above named 

 from the primitive towards the north-east, we shall find 

 that it passes between Martha's Vineyard and the conti- 

 nent, and crosses Cape Cod, leaving us to conclude that the 

 Vineyard and Nantucket are a continuation of that exten- 

 sive formation, hitherto called alluvial, of which Long-lsl- 

 anh has been regarded the north-eastern limit. If we pro- 

 long this curve still further, it will include within it Nova 

 Scotia, and, at least, a part of Newfoundland. Here we 

 are reminded of the vast sand banks along that coast, and 



* The remarks of Mr. Finch, (who appears to be ocenlarly acquainted 

 with similar formations in England,^ on the tertiary formations of North 

 America in Vol. VII No. I of the Journal of Science, tend very much to re- 

 move these doubts, and to establish me in the belief of the existence of the 

 Plastic Clay Formation in the Vineyaid. I feel indebted to that gentle- 

 man for the important hints he has thrown out. 



