182 
Island. In like manner, 108, on the east side of this headland, 
is exactly in line with a large dike near the southern end of 
Brush Island. 
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Fic. 17.—PLAN SHOWING A GROUP OF INTERSECTING DIKES 
ON THE CoHAssET Rocks. SCALE, I INCH = 50 FEET. 
Crossing Sandy Deach, we come at once, on the north side 
of Beach Island, to 104 and 105, which can be traced for long 
distances, the latter enclosing, near the eastern shore, a long 
narrow mass of granite. The second dike beyond (107) is 
slipped about twice its width. The large dike south of the 
artificial harbor divides eastward into two unequal branches 
separated by from 8 to 10 feet of granite; and 15 feet north of 
it is a one-foot branch. ‘The composite dike (109) on the east 
side of Beach Island is near the contact of the coarse typical 
granite and the mixed granite and diorite. The intersection of 
111 by 110 (Fig. 18) is a clear case of the confusion of the 
first and second systems. The intersection is very oblique, 
extending over 20 feet along 111. Immediately north of 110 
is an unenumerated six-inch dike. The next dike (112) is a 
fine and instructive example of a branching fissure, and shows 
flow-structure parallel with the walls. 
The dike on Hog Rock (129) is exposed again in the 
re-entrant angle of the shore south of Strawberry Point. The 
next dike (130) is beautifully porphyritie, with large clustered 
