29 



blendic, typical granite, already mentioned ; (2) a finer-grained, 

 less hornblendic, euritic variety, sometimes approaching petro- 

 silex ; (3) the very hornblendic, commonly fine-grained granite, 

 which is usually poor in quartz and frequently passes into 

 diorite. 



1. The coarse, typical granite above described, well known 

 in Quincy, where it is so extensively quarried, may be traced 

 the entire length of the Blue Hill range ; but with greatly di- 

 minished breadth towards the west. Westerly, it is limited to 

 the northern side of this group of hills, and at no point does it 

 appear to reach their southern border. A fine example of the 

 typical granite forms the northern shore of Cohasset Harbor ; 

 and it is the prevailing variety in Cohasset and Hingham. In- 

 deed, judging from the observations of myself and others, and 

 the specimens collected by Prof. Hitchcock, and now in the 

 State cabinet, I conclude that the broad area of granite which 

 sweeps through northern Plymouth and Bristol and southern 

 Norfolk Counties, is mainly, and towards its eastern end almost 

 entirely, composed of this variety. In the northern part of 

 Plymouth County, south-east of a line drawn from Scituate to 

 Abington, rock outcrops are few and far between, and the 

 granite marked on the map as occurring in Kingston, Duxbury, 

 Marshfield, etc., is largely conjectural. I have seen no indica- 

 tions, however, of the existence here of any other rock ; and 

 hence I have ventured to color the entire area as granitic, in- 

 stead of employing the general Huronian color, which would, 

 perhaps, have been the wiser course. I suppose that this granite 

 is mainly of the typical variety. I have observed this kind in 

 situ in Marshfield ; and Mr. Elmer Faunce reports an exposure 

 of the same rock on Jones River in Kingston. 



At some points in this southern region the coarse granite is 

 porphyritic with feldspar crystals. Prof. Hitchcock 1 mentions 

 several localities, and I have observed a good example on Thax- 

 ter Street in Hingham. It is always of local extent. The 



1 Final Report Geol. of Mass., p. 669. 



