134 The American Geologist- March, isno 
last-named is very subordinate, and by no means as abundant 
as in the bosses. The dikes are therefore relatively acidic ; 
and if that implies, as is doubtless true, that they were rel- 
atively fluid when molten, we can the more readily understand 
the distance to which these narrow bodies have penetrated 
from the parent mass. The minerals afford nothing notable 
themselves. An occasional apatite inclusion is about the 
only additional component that catches the eye. There is no 
glassy material whatever. The average crystals are from one 
to five m.m. But with them are to be seen larger crystals of 
orthoclase, as much as five c. m. in length by one c. m. broad, 
— which give the dike somewhat the aspect of a granite- 
porphyry. The phenomena cited above agree in all essen- 
tials with those mentioned by Rosenbusch in describing granite 
dikes, (Mikros. Phys, vol. i. p. 279) and from this reference we 
may see that similar phenomena are known at Killiney in 
Ireland, and in the tin district of Saxony. 
The granite dikes and the bosses not infrequently include 
in their mass fragments of the country rock. This consists of 
rather thin-bedded mica schist and quartzite, and the included 
fragments give us one of the surest indications of the intrusive 
character of the granite. The walls on the contact with the 
dikes and the included masses are very generally finely crys- 
talline aggregates of biotite and quartz. The individuals are 
only 1-20 mm. in breadth, by 1-5 mm. long, and lie with axes 
parallel to the contact, as if a great pressure had forced them 
to take such a position. They seem to correspond with the 
commonest contact minerals present on the edges of the 
Cortlandt series,^ on the east side of the Hudson, and slides in 
the writer's possession from the contact schist on Stony Point 
on the west side, are very similar. 
On the eastern side of cape Arundel, near dikes 84 and 35, 
the schists have been much shattered and fissured. The cracks 
have been subsequently filled with vein matter which closely 
resembles a granite. It consists of quartz, orthoclase, silvery 
muscovite, and tourmaline. The resemblance to the small 
tin veins of Cornwall and Saxony, Virginia and Maine, ^ is 
•^C. T. .Jackson, Proc. Bost. Soc. Nat. Hist. vol."xii, p. 267. 1869. 
T. S. Hunt, Inst. Min. Eng. vol. r, p. 373. 
W. P. Blake. Mineral Resources, 1883-84, p. 597. The figure of the 
tin veins at Winslow, Me., given by Blake on p. 598 is a perfect repro- 
duction of the veins here, substituting tourmaline for cassiterite. 
^ G. H. Williams, Am. Jour, xxxvi, j). 256. 
