Dodge.] 
214 
[May 18 . 
The relations of the granite to the newer felsites and the older 
schists has been too well stated for the subject to be enlarged upon 
here. The relation between the various granites has never been 
determined. At Gloucester, granite ledges awash on the shore 
behind the Pavilion contain inclusions. In the granite of Kettle 
Island, off Magnolia, are inclusions, some of which appear to be 
of stratified rock. 
There does not appear to be on the North Gooseberry any of the 
brecciated rock so often closely associated with the simple variety 
north of Boston and at Mattapan, in which small irregularly shajied 
fragments of distinctly banded felsites are massed together, with 
the bandings of the several pieces at all angles to each other. A 
possible cause of this condition (which writers do not seem to dis- 
tinguish from the sedimentary aggregation of felsite fragments) 
is suggested by the phenomenon which observers of modern vol- 
canic outbursts record, of cooled and hardened portions falling 
from the top of the rolling lava-wave into and beneath the yet hot 
and liquid mass which receiving or covering them rolls on until 
itself cools. 
The felsite of the North Gooseberry, in marked contrast with 
the brilliant deep colors of the Mattapan felsite, is partly dark gray, 
partly of a light reddish tint. In one place a small dike of dull 
black with a direction of N. 60° E. (that of one set of joints), 
doubling its width in a few feet, cuts the redder rock. 
A dike of diabase ?, two and a half feet thick, cuts through the 
felsite in the North Gooseberry with direction N. 30° E. It has a 
low south-easterly dip. This dike may probably be traced beyond 
the limits of the island. It is highly magnetic and appears to 
vary in character, being partly crystalline, partly of amorphous 
texture. 
“ Basalt Dikes ” 1 The direction, at the surface, of the dikes 
which penetrate the stratified rocks about Boston and certain 
other eruptives associated with these, vary widely, and they usually 
1 Mr. Wadsworth has quoted me as asserting the Jiornblendic nature of certain intru- 
sive rocks of this vicinity, especially the Somerville dolerites. (Proceedings, Vol. xix, 
pp. 227, 236). Undeniably, I called them hornblendic, but the purport of my paper 
differed from his. Many of the basic rocks of this vicinity are conspicuously augitic 
