Crosby.] 
508 
[May ig, 
series ; and the latter is exposed continuously for a thickness of 
fully 500 feet. Between the granite north of Beal Street, which 
still holds its normal relations to the bedded rocks deposited upon 
it, and the granite against which they end, as the result of 
faulting, on the south, we have then a steep monocline and one 
complete section of the Hingham strata. From the Home Meadows 
to Beal’s Cove there was originally, or would have been but for 
the faulting, one continuous syncline. This is broken transversely 
by the Hockley Lane fault. The western half remains an open 
syncline; but the greater part of its southern slope is carried away 
by a strike fault, which brings up the underlying granite in that 
direction. The eastern half, owing to the stronger compression, 
becomes an inverted isocline, with the axial plane dipping to the 
south ; and its northern side is partly carried away and partly 
concealed by a strike fault, bringing up the granite axis, which 
these strata once covered, and which is obviously a dominant or 
controlling factor in the structure of the bordering strata. 
Although the map appeared to afford at the time of its con- 
struction the best interpretation of the scattering outcrops around 
the western extremity of the granite axis, it is now regarded as 
more probable that all the beds curve regularly around the axis 
and that the structure of the beds on both sides of the axis is 
monoclinal, the northwestern monocline being complicated by strike 
faults, repeating the band of melaphyr. This second belt of 
melaphyr is a direct prolongation of the great body of melaphyr 
lying east of Huit’s Cove, and cannot be regarded as intrusive. 
The general interpretation of the geological structure here pro- 
posed makes it unnecessary to suppose that any of the Hingham 
strata extend far into Weymouth, and tends to emphasize the im- 
portance of Weymouth Back River as a geological boundary ; 
and we may reasonably assume that this valley follows a fault 
comparable in magnitude and structural importance with that 
along the east side of Hingham Harbor, separating .areas which 
are strongly contrasted in their geologic features. 
CROW POINT AND HUIT’S COVE AREA. 
This area (PI. XVI) is divided into two quite distinct parts by 
the great dike extending west from Downer Avenue to the eastern 
angle of the Huit’s Cove melaphyr. The southern part is, as we 
