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have thus fiuilted walls and many of the normal features of 

 more important examples. Slate Island is, indeed, a fine field 

 for the student of structural geology : and it is interesting to 

 observe in this connection that the conditions are unusually 

 favorable for obtaining cabinet specimens of the slate exhibiting 

 its various structural features ; for besides the debris w^hich 

 naturally encumbers the shore, we have that afforded by the 

 numerous small quarries scattered over the island, the slate 

 having been extensively quarried in the past for ballast. 



The half-tide ledge southwest of Slate Island is composed 

 of slate precisely similar to that on the island, with a nearly 

 vertical southerly dip. The bed rock of Grape Island is 

 exposed at only two points, on the north and south shores, 

 near the eastern end of the island. The southern ledge, which 

 is in the line of strike of the north shore of Slate Island, is a 

 dark gray to black, thin-bedded, and fissile slate. The cleavage 

 conforms perfectly with the bedding, and the slate is well jointed. 

 The strike is N. 75° E. and the dip S. 80°-90°. The slate is 

 somewhat contorted in places, and it is traversed by several small 

 irregular gray dikes similar to those of Slate Island. The 

 northern ledge, which is on the extreme northeast corner of 

 the island, is quite extensive at low tide. It, also, is all slate ; 

 l)ut mostly a coarse, gritty, gray variety, and not, as a rule, 

 very distinctly bedded. Toward the northern end of the ledge, 

 however, it is darker and softer, and more like the slate on the 

 south shore. The strike is N. 70° E. ; and the dip S. 70°-75°. 



Beyond these islands there are no outcrops of any kind 

 nearer than Raccoon Island on the west, the villag-e of Hull 

 on the north, and Kocky Neck on the east. Hence we can 

 only speculate as to the extension and probable relations of 

 the newer slates in those directions ; but southward there can 

 be no reasonable doubt tliat they are continuous with the 

 similar slates formin<>; the north shore of Hinoham. Unfortu- 

 nately, however, the vertical position is a very equivocal one ; 

 and it is quite impossible to say with certainty whether in 



OCCAS. PAPERS n. S. N. II. IV. 17 



