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, Inthe 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 currents,into 
this their retired bosom. J 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 L 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 hy pothe- 
sis. In short, although this partof the island is coloured as 
alluvial, 1 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 the entire ab- 
sence of diluvial detritus, so abundant in every other part yf 
_ 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- 
tuin this is identical, it must, for the present, be denomina- 
ted alluvial, © 0 bans . 
2 Diluvial. 
This formation invests, in a very conspicuous manner, 
the whole of the Vineyard, with the exception of the part 
justdescribed. All the north western extent of the island, 
several miles in width, is ‘hilly ‘and tineven: 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. ‘PF should judge that ir some 
places. ihis rises. three hundred, or even four bundred 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 
anitic, and of course, of a’ white colour; so that they may 
Seen at a great distance to good advantage. I had no 
