Dikes near Portland, Maine. — Lord. 345 
containing nearly 2 per cent, less AU O^, and SiO; than the 
anorthoclase from Tyveholmen (II), is much closer related to 
this variety of feldspar than to the murchisonite from Ula 
(III). It appears that the latter mineral, from its high per- 
centage of SiOs (64.96) and K^O (5.84) combined with but 
1. 19 per cent CaO, contains a larger amount of the ortho- 
clase molecule than either of the other two. 
The chemical relationship of the camptonyte (IV) to the 
augite-porphyryte from Kennebunkport (VI) is closer than 
that of the enstatite-diabase -porphyry (\') which occupies in 
a certain sense an intermediate position between these two, 
although containing more ferrous iron and magnesia. 
From what has been said it appears that the basic dikes 
in the neighborhood of Portland vary in mineral composition 
from an enstatite-diabase-porphyry, containing enstatite, diop- 
side, plagioclase and magnetite, to a camptonyte, composed of 
olivine, hornblende (barkevicite), anorthoclase, and accessory 
augite. 
These basic intrusions are almost in a direct line of strike 
with those from Kennebunkport and Bald cliff, and as the 
main rock-types from the three areas are (with the sino-le 
exception of the enstatite-diabase) essentially identical miner- 
alogically and chemically, there seems scarcely anv doubt of 
their genetic relationship. 
The chemical affinity of the brown hornblende and anor- 
thoclase of the camptonyte, with the barkevicite and soda- 
feldspar of augite-syenite from Norway has been pointed out 
(see pages 343-344), and it is therefore possible that some 
at least of the basic dikes from the Maine coast are ofifshoots 
from an underlying parental rock of this description. It 
is suggestive in this connection to note the occurrence of large 
inclusions of augite-syenite in a cam])toriyto dike from Kenne- 
bunkport.* 
This syenite is of a pinkish gray color, somewhat mottled, 
owing to dark areas of magnetite and augite scattered through 
the flesh colored, granular feldspar. Originally the rock 
was composed of orthoclase. green augite (diopside) with 
some magnetite and apatite, but subsequent fusion and re- 
*Probably dike 64 of Kemp. op. cit., p. 131. 
