Geology of Martha's Vineyard. 245 



and I could hardly believe the inhabitants who told me, 

 that no rocks were found in place on the island. But 

 wherever 1 had an opportunity to examine, these ledge like 

 appearances vanished on a nearer approach ; and the dilu- 

 vial character of the surface became manifest. So that I 

 feel a good degree of confidence, that the same will be 

 found to be the case, with those eminences, that 1 did not 

 visit. These loose stones vary in size, from that of the 

 smallest pebbles, to that of masses, ten or even fifteen feet 

 in diameter. They are almost without exception, of a 

 primitive character ; consisting of granite, gneiss, mica 

 slate and quartz. I saw a few masses of a pudding stone, 

 similar to that of Roxbury ; but no other secondary rock. 

 In short, the detritus of this formation appears obviously, 

 to have been derived from the rocks, that occur in place 

 along the coast, on the mainland. 



The thickness of this diluvial mantle is not great. The 

 sand from the plastic clay formation beneath it, is indeed so 

 mingled with this, as to give a predominant character to the 

 soil, and even the clay beneath the sand, is sometimes seen 

 at the surface. In some tracts of considerable extent, little 

 else, but the sand is seen : the diluvial bowlders and peb- 

 bles being very rare. It is obvious from this description 

 that the soil of the island must be very light and poor, and 

 so indeed it is. Some fertile tracts, however, occur along 

 the margin of the small streams, or brooks, and also in some 

 instances, in the immediate vicinity of the sea: and proba- 

 bly the soil in general, is of much the same character, as that 

 along the adjacent shores of the continent. 



The character of the diluvium of the Elizabeth islands, 

 appeared so precisely like that of the Vineyard, that I have 

 no doubt of their indentity I say appeared, fori did not 

 land on these islands ; but having passed among them at 

 two places remote from each other, and approached often 

 within a few rods of the shore, I could not but be struck 

 with their exact resemblance to the Vineyard, in the con- 

 tour of the hills and vallies, in the colour, size, and quanti- 

 ty of the bowlder stones, in the sandy aspect of the soil, and 

 in the high sloping sand banks so frequent along the shore. 

 I have accordingly coloured several of these islands on the 

 subjoined map as diluvial. It may be thought I do this on 

 very slight grounds, but as I have plainly stated what those 



