342 The Amaican Geologist. December, i89S^ 
FesOs 498 8.92 
FeO 10.09 
MgO 6.67 5.30 
CaO 9-88 9.82 
Na=0 3.52 4.34 
K2O 62 1.42 
H.O 87 .69 
100.22 100.75 
The chemical similarity of these rock-types is apparent. 
The augite-porphyryte, or diabase-porphyry as it has been 
called in this paper, is somewhat richer in alkalies and alum- 
ina, and poorer in iron and magnesia than the enstatite-dia- 
base-porphyry, which can be explained by considering the 
fact that the latter rock contains relatively less feldspar, and 
more ferromagnesian constituents than the angite-porphy- 
ryte. 
Camptonyte is represented by dike 8 and 9. This rock 
has formed the topic of considerable discussion since it was 
first described by Hawes* under the name of dioryte. The 
broader significance of the term as applied by Rosenbuscht 
has been modified by American authors — notably Kemp and 
Marsterst- — to embrace only such varieties of diabasic dike- 
rock in which hornblende predominates. An appreciable 
amount of augite gives rise to an intermediate type — augite- 
camptonyte.§ 
Adopting this latter classification we have but one dike 
of true camptonyte (8), No. 9 being augite-camptonyte. The 
camptonyte dike (8) occurs at Portland head-light on the east 
coast of cape Elizabeth, cropping out again on the western 
shore just beyond the map border. It is about six feet thick, 
stands almost vertical and has the prevailing N. 55° E. strike 
of the adjoining dikes. 
*G. W. Hawes: On a Group of Dissimilar Eruptive Rocks at 
Campton, N. H. Am. Jour. Sci., Ser. III., Vol. XVIL, p. 14. 
fH. Rosenbusch: Massige Gesteine, 3te Aufiage, pp. 535-550. Stutt- 
gart, 1896. 
%]. F. Kemp and V. F. Marsters: The Trap Dikes of the Lake 
Champlain Region. Bull. 107. U. S. Geolog. Survey, p. 30. 
§For literature on camptonyte see V. F. Marsters: Camptonite and 
Other Intrusives of Lake Memphremagog. Amer. Geologist, Vol. 
16, 1895. Page 35-36. 
