Dikes near KeiwiehunJcport, Maine. — Kemp. 137 
88), while in a few the olivine seems to fail, and their charac- 
ters are more of the augite porph3'rites (Nos. 33, 90, 92). In 
one the basaltic hornblende is the most notable of all the con- 
stituents, and of itself the dike would be a hornblende porphy- 
rite (No. 25), such as in the writer's estimation would place it 
in the series of typical camptonites. This is the most inter- 
esting, as showing here such a close parallel to the original 
camptonites of Hawes, at Livermore Falls, N. H. (Amer. 
Journ. Feb. 1879). There, as well as here, diabase and olivine 
diabase occur with the dioritic rock in parallel dikes, but 
while hornblende is there the rule, here it is the exception. 
Rosenbusch, in a review of Hawes' paper (Mikros. Phys. B. I. 
p. 333) groups all of the Campton dikes under the one name 
Camptonite, considering the variations in mineral composition 
not sufficient to separate them sharply. While that is a just 
and fair view, the abundance of the small basaltic hornblende 
crystals in the Campton dykes, and in the various others 
which have come to light since,' should make its presence the 
chief diagnostic feature of a camptonite. The writer would 
not consider these normal olivine diabases of Kennebunkport 
as true camptonites, but rather, that from some exceptional 
circumstances of composition or cooling, one or two of the 
dikes had crystallized as such and several had approximated 
it. 
The idiomorphic minerals of these porphyrites do not es- 
sentially differ from those described in the holocrystalline ex- 
amples. The ground mass in the very narrow forms is glassy 
but not very transparent, on account of multitudes of in~ 
elusions. In the broader ones, and especially 92, the base is 
microcrystalline, and mostly made up of very minute plagio- 
clase rods. Such rods appear in all these latter dikes, often 
distributed through a relatively abundant ground-mass. The 
glassy structure is sometimes developed in the edges of dikes 
whose centre and largest part is holocrystalline. A slide from 
dike 27 exhibits the wall as a mass of quartz and pyrite, — then 
aporphyriticstripS mm.wide,-then avery finely crystalline in- 
terior. The borders are in each case sharply marked. This 
may be explained by the partial fusion and involution of the 
wall, 'and by quick cooling, but when dikes one and two feet 
'B. J. Harrington, Geol. Surv. Canada, — 1877-78, p. 4.59. 
J. F. Kemp, Amer. Jour. Apr. 1888. Amer. Naturalist, Aug. 1888; 
the same, and V. F. Marsters, Amer. Geol. Aug. 1889. 
