242 Geology of Martha's Vineyard. 



ately struck with the idea, that this sandy desart must have 

 been formed by the action of the waves of the vast Atlantic, 

 which have beat upon this shore, without obstruction, for so 

 many centuries. In the south westerly part of the island, 

 the high perpendicular cliffs indicate that the waves have 

 encroached upon the hilly part of the island; and it would seem 

 not altogether improbable, that the sands and clays, thence 

 worn down, might have been driven by tides and currGnts,into 

 this their retired bosom. I am aware, however, that no in 

 stance is known, in any other part of the world, of so ex- 

 tensive an alluvial deposition from this cause : and perhaps 

 if I had been able to spend more time in its examination, 

 especially its south eastern margin, I might have discov- 

 ered positive proofs of the incorrectness of such an hypothe- 

 sis. In short, although this part of the island is coloured as 

 alluvial, I am strongly inclined to believe, that it is referable 

 to an older and distinct formation. Its inferior level, how- 

 er» the perfect evenness of its surface, and »he entire ab- 

 sence of diluvial detritus, so abundant in every other part of 

 the island, clearly discriminate this from the Plastic Clay 

 Formation, about to be described. But as 1 am not pre- 

 pared, even to conjecture, with what other European stra- 

 tum this is identical, it must, for the present, be denomina- 

 ted alluvial. 



2 Diluvial. 



This formation invests, in a very conspicuous manner, 

 the whole of the Vineyard, with the exception of the part 

 just described. All the north western extent of the island, 

 several miles in width, is hilly and uneven : with no abrupt 

 precipices, however, but rising into rounded eminences, 

 which together constitute a ridge of considerable extent, and 

 nearly as long as the island. I should judge that in some 

 places. :'his rises three hundred, or even four hundred feet 

 above the ocean ; and the quantity of huge bowlder stones, 

 scattered over these hills on every side, is immense. The 

 land is mostly cleared, and the rounded masses are chiefly 

 granitic, and of course, of a white colour; so that they may 

 be seen at a great distance to good advantage. I had no 

 doubt, for a time, that the bowlders I saw so numerous, and 

 so large, on the remote hills, were ledges of granitic rocks ; 



