— 
107 
It can be traced almost to the northern shore of the bay; but no 
trace of it could be found in the almost continuous ledges of 
granite on the south shore. Its last observed course, however, 
would сату it directly up the mouth of Weir River; and 
the absence of additional outerops is not, therefore, evidence of 
an important displacement. That this great dike should not, 
on account of its trend, be referred to the third or newest 
system of diabase dikes is obvious not only from its lithological 
character, but also and especially from the fact that it is clearly 
eut by, and hence is older than, one of the east-west diabase 
dikes (39), the outcrop of the latter continuing directly 
through the melaphyr dike. 
The Diabase Dikes. 
The occurrence of the diabase dikes in three systems — two 
older systems having approximately east-west trends and a 
newer north-south system — has been noted; and also the fact 
that the east-west systems form three belts, corresponding in a 
general way with the principal dislocations of the district. All 
of the dikes agree in direction with well-determined faults, 
although often not actually coinciding with a fault of sensible 
displacement. The two east-west systems are certainly much 
more closely related to each other than to the north-south 
system, and since, in the absence of clearly exposed intersec- 
tions, they are not always readily distinguished, it appears best 
not to attempt to. describe them separately ; but we will, 
instead, follow the classification by belts, commencing with the 
northern or coastal belt. 
Although Mr. Merrill has not observed any marked or 
constant difference in mieroscopie characters between the older 
or east-west dikes and the newer or north-south dikes, they are 
usually somewhat contrasted in external aspect. The east-west 
dikes are commonly of a dark greenish gray color, due to the 
abundance of secondary chloritic minerals and epidote. They 
are, relatively, chemically stable, resisting atmospheric influ- 
