338 The American Geologist. December, 1898 
of the area studied. They form a very conspicuous feature 
of the coast, partly on account of their dark color, which gen- 
erally stands oyt in strong contrast to the lighter grav tints 
of the schists, but especially owing to the fact that thev 
weather out more rapidly than the surrounding rock, leaving 
straight channels with vertical walls to mark their original 
location. 
They belong, with a single exception, to one general series 
with a very persistent N. 55° E. strike, and essentially vertical 
dip. This conformity in strike with that of the schists is in- 
dicated on the map. These dikes rarely exceed six feet in 
thickness, and are usually from only two to four, but thev 
frequently can be traced for considerable distances along the 
coast; thus No. 14, at Broad cove, cape Elizabeth, possessing 
peculiar mineralogical characteristics, is easily recognized 
again on Bailey's island, a distance across the bay of nearly 
fourteen miles. 
The exception referred to is a dike 80 feet thick, of a 
coarse grained enstatite-diabase-porphyry, occurring on the 
eastern side of Cousin's island, and extending across the 
southern end of Littlejohn's island in a general easterly di- 
rection. 
The prevailing character of these intrusions is dense por- 
phyritic. with occasional coarser crystalline varieties, depend- 
ing upon the physical conditions under which the rock-mag- 
ma solidified. The walls of the dikes in direct contact with 
the schists are aphanitic, and in some cases almost vitreous, 
whereas in the central portions, especially of the larger dikes, 
a coarser texture prevails. Even granular varieties are not 
frequent. (7, 10, 17, 24, 26.) 
The mineral composition of the rock in general is that of 
olivinc-diabasc-porphyry , consisting of olivine, augite, plagio- 
clase and magnetite. Subordinate types, containing as diag- 
nostic constituents enstatite or hornblende, will be classed as 
enstatite-diabase-porphyry and camptonyte respectively. 
Previously to the intrusion of the diabase and camptonyte 
occurred that of granitic rock. A large pegmatyte dike (32) 
with aplitic extensions (31) forms a part of the western shore 
of Biber's island, and can be followed in a northeasterlj^ direc- 
tion through Pettingill's, Williams' and Sister island to Mare 
