470 Scientific Geology. 



of this latter rock are so accumulated upon the granite, and the coun- 

 try is so nearly level, that it is impossible to ascertain the limits of 

 the two rocks. As we go easterly into the region of the Middlebor- 

 ough ponds, the difficulty increases ; and I have put down an exten- 

 sive patch of diluvium in that quarter on this account. In the vicinity 

 of New Bedford and Rochester the same difficulty has perplexed me 

 in ascertaining the limits between granite and gneiss. Nor shall I 

 be disapointed if the lines which I have finally settled upon shouV 1 

 need material alteration. 



It will be seen that I have connected the Fall River range of gran- 

 ite on the east, with the sientic granite in Cohasset, Hingham, <^*c. 

 Two facts have led me to do this. In the first place, as we pass from 

 Marshfield through Pembroke, Plympton, and Carver, to Wareham, 

 we do occasionally meet with a ledge of granite : and secondly the 

 bowlder stones are nearly all granite. It will be seen, however, that 

 a great part of this region I have marked as diluvial. 



The map will show, also, that I have extended a strip of granite 

 from Plymouth into Barnstable county as far east as Brewster, and 

 carried another branch into Falmouth. These ranges follow the 

 highest ridges in the south part of Plymouth and in Barnstable coun- 

 ties. And although in no part of these ridges, with one or two excep- 

 tions, have I found rocks in place, yet such is the size and number of 

 the bowlders as to satisfy me that they have never been far removed 

 from the parent rock ; and I cannot but believe that ledges do exist a 

 little below the surface ; and not improbably in some places, which 

 have not fallen under my notice, they may be found at the surface. 

 Where first Cape Cod commences, and nearly half way between 

 Sandwich and Falmouth, appearances are peculiarly indicative of 

 granite ledges : and they continue nearly to the village of Falmouth. 

 As we go eastward they are less striking, until we reach the town of 

 Brewster, where, as I have shown under diluvium, there is reason to 

 suppose the shattered crest of a ledge appears. 



I am aware that it would have been accordant with truth to have 

 colored the whole of Cape Codas diluvial. But my rule has been 

 not to exhibit that stratum when I could ascertain the rocks beneath 

 it. Others must judge, whether the evidence of the existence of gran- 

 ite in place in the region under consideration, is probable enough to 

 justify me in the course I have taken. 



That gneiss range in the central parts of the State, which lies east 

 of the Worcester mica slate, abounds in veins and protruding masses 



