Crosby.] 
114 
[December 15 
numerous large and small, irregular, angular, contorted and 
indurated masses of slate. On the north-east corner of the Head, 
there is quite a large development of slate, but it is broken through 
in every direction by the diorite. The slate is mainly on top of 
the diorite, taking a general view. The diorite is all thoroughly 
intrusive, but it has been erupted at different periods, as dikes of 
diorite cut both diorite and slate. 
At only one point, so far as I have observed, is the slate pene- 
trated by the granite. This is on the northern end of Stave 
Island. The granite occurs in irregular masses as well as small 
and tortuous dikes. Its contact with the slate is typically igneous, 
the granite penetrating the slate repeatedly and enclosing large, 
angular fragments of that rock. The granite is not very coarse, 
and is mainly of a lively pink color, though some of it is white. 
This is undoubtedly a very exceptional phenomenon, and I do 
not believe that the great masses of granite on this coast have 
been erupted since the deposition of the slate, but they are older. 
The granite on Stave Island appears to bear to different parts of 
the diorite the double relation of an intersecting and intersected 
rock. 
Undoubtedly one of the most important problems presented by 
this slate formation is the determination of its age. Nearly 
twenty years ago Prof. C. H. Hitchcock suggested, 1 on the ground, 
as he states, of fancy rather than real argument, that the siliceous 
slate or quartzite at Bar Harbor belongs somewhere in the Lower 
Silurian (Cambrian) ; and in 1876 he still held the same view 
describing this formation as “ probably of Cambrian age.” 2 His 
description of the rocks on Flint and Ship Islands, in Narraguagas 
Bay, some twenty-five miles east of Bar Harbor, is also of interest 
in this connection, 3 and a few lines may be quoted. “ The rock 
upon Flint Island consists of layers of flint and hornstone of dif- 
ferent colors and textures. Some layers are flinty sandstone, and 
others are somewhat calcareous. Upon Ship Island, a short dis- 
tance west of Flint Island, the layers are much less flinty, being 
1 Second Annual Report upon the Natural History and Geology of the State of 
of Maine, 1863, p. 270. 
2 Geology of New Hampshire, Vol. ii, p. 32. 
3 Sixth Annual Report, Maine Board of Agriculture, 1861, p. 233-4. 
