Seituate is to determine to what extent they сап be referred to 
the same systems as the Nantasket dikes. Systematie observa- 
tions for this purpose were confined to the immediate vicinity of 
the shore ; and the following paragraphs and aecompanying lists 
give the results of a complete canvass of the littoral dikes from 
Green Hill to the shore beyond the Glades. No attempt has 
been made to trace any of the dikes inland or beyond the clean 
exposures afforded by the waves ; but such casual observations 
as have been made away from the shore indicate that the littoral 
zone is, in the number and trends of the dikes, representative of 
the entire area. No dikes have been represented on the general 
map, partly on account of the inconveniently small scale, but 
chiefly to avoid giving the impression of great inequality in the 
distribution of the dikes, 
It is readily apparent that the dikes of Cohasset and Scituate 
exhibit a general agreement in character and trend with those 
of Nantasket. No dikes of melaphyr have been certainly 
identified ; but in their place, as previously explained (page 
105), there is a well-defined series of porphyrite ‘dikes. These 
are clearly older than all of the diabase dikes and probably date 
from the Nantasket flows of porphyrite. Each of the three 
systems of diabase dikes is clearly represented, and the ex- 
posed intersections show that their relative ages are essentially 
unchanged. But the oldest system, having the normal trend 
N. 75° to 80° E., largely predominates, though, as at Nantas- 
ket, it cannot always be clearly distinguished from the.second 
system, with the normal trend S. 75° to 80° E. Only a few 
dikes ean be referred to the second system. The dikes of the 
newest or N.—S. system also are relatively less numerous than 
in the Nantasket area; and it is especially noteworthy that they 
become less numerous eastward, not a single clear example 
having been observed beyond the Cohasset Rocks or more than 
three fourths of a mile east of Green Hill Beach. This 
apparent limitation of the newer dikes to the Nantasket area 
and its immediate vicinity is an interesting and suggestive fact, 
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