Crosby.] 
112 
[December 15, 
The slate, especially on the north and west sides of the bay, 
where it lies nearest the crystalline schists, is often finely mica- 
ceous. The mica is in an exceedingly fine state of division and is 
never conspicuous. It is certainly not usually, and probably never, 
indigenous in the slate, as some observers have supposed ; but sim- 
ply indicates the derivation of this rock from the Huronian mica 
schists. In fact, the slate and schists appear to be almost identi- 
cal in composition. 
Although embracing no beds of coarse material, like conglom- 
erate, it is yet very clear that the slate is a shallow water deposit. 
Proofs of this are found in the strong resemblance in composition 
just noticed between the slates and the immediately adjoining 
crystallines, in their variable character, and in the eroded mud sur- 
faces, and ripple and rill marks which have been observed in vari- 
ous parts of the bay, but especially on Hawthorne Island (formerly 
Hog Island) on the east side of the bay. The conditions under 
which the slate was deposited appear to have been very similar to 
those which obtain here at the present time; i. e., Frenchman’s 
Bay was then, as now, a tranquil, shallow sheet of water deposit- 
ing little or no coarse sediment. There are very few, and no 
extensive, gravel beaches in the modern Frenchman’s Bay, but the 
sediment now consists almost entirely of fine sand and impalpa- 
ble mud or clay. 
The slate is rarely highly inclined, the dip ranging generally 
between 15° and 30°; but, what is more important, it is nearly 
always away from the nearest shore of the bay. Thus on Wau- 
keag Neck and Seward’s Island, which lie across the northern end 
of the bay, the dip is southerly ; on Calf Island and Hawthorne 
Island, situated in the north-east corner of the bay, the dip is 
south-west ; while at Bar Harbor, on the south-west side of the 
bay, the dip is north-east. The general plan of the structure of 
the bay is quaquaversal, the strike and dip of the slate being 
everywhere determined by the general trend of the nearest shore, 
except that the slate dips north and north-west from the belt of 
islands lying between Bar Harbor and Gouldsborough, indicating 
the existence of an anticlinal here dividing the bay into two 
basins. 
