68 
(Fig. 8). Commencing at the north end, the first ledges of 
conglomerate and melaphyr rise somewhat abruptly from the 
marsh and the bay immediately south of the great east-west 
fault, and about five hundred feet, following the railroad, south- 
west of the broad, low outcrop of red and green slate or slaty 
tuff already described ; and, as the map shows, the section is 
almost uninterrupted along the east side of the railroad from 
this point to the south side of Marsh Island. 
Melaphyr. Conglomerate. 
Fic. 5.—SECTION SHOWING THE FAULT-DIKE (25) AND THE CONTACT 
BETWEEN THE THIRD CONGLOMERATE AND SECOND MELAPHYR, 
SOUTH OF THE FAULT. SCALE, I INCH = 30 FT. 
It begins with the typical melaphyr of the central area, a 
dark green, evidently basic and highly amygdaloidal variety. 
The amygdules are not uniformly distributed ; but they are 
especially abundant in a superficial layer of the rock from two 
to three feet thick. They are usually somewhat elongated and 
have a distinctly linear arrangement parallel with the layer; so 
that the flow-structure of the melaphyr as a whole is very marked. 
This mass of melaphyr has an exposed breadth of about forty feet 
north and south and is divided midway by dike 26 ; while it is 
abruptly terminated on the south by dike 25. This dike un- 
doubtedly marks an east-west fault; for it is bordered by con- 
glomerate on the south (Fig. 5). The fault probably hades 
with the dike to the north, and the melaphyr is clearly on the 
downthrow side. Not more than eight feet in thickness of the 
conglomerate are exposed before it is overlain by melaphyr. 
