THE ARCILEAN ROCKS. 



467 



entirely. The upper sand- 

 stone layers are coarse and 

 brownish-colored, and lie in 

 large, flat slabs, giving the 

 river bed, for many rods, 

 the appearance of a paved 

 street. 



On the line A B of the 

 map, a section was meas- 

 ured across the stream, 

 which is shown in Fig. 4. 

 At the southeast end of this 

 section a vertical cliff of 

 heavily bedded sandstone, 

 35 feet high, forms most 

 of the river bank. Be- 

 neath the sandstone, 

 gneiss shows for about 5 

 feet down to the water's 

 edge. Its upper portions 

 are altered to a soft kaolin, 

 about 2 feet in thickness. 

 Immediately at the foot of 

 the cliff runs the main 

 channel of the river, here 

 about 400 feet in width. 

 Beyond it to the northwest, 

 a series of low outcrops of 

 gneiss alternate with nar- 

 row water channels across 

 the remainder of the river 

 bed. The first exposure 

 beyond the main channel 

 was not reached. The next 

 showed a coarse - grained, 

 pink- white-and-black-mot- 

 tled, quartzose, gneissoid 

 granite (864), striking N. 42 E., and dipping north- 

 westward 70, with marked bedding planes. A second 

 set of joints, much less marked, strikes N. 50 W., 

 and dips 80 N. E. The quartz of this rock is hyaline, 

 and in fine grains aggregated into large blotches; the 

 mica is blackish and fine-grained, and aggregated along 

 certain lines; and the felspar is both white and pink, in 

 large facets. The weathered surface is brownish and dull, 

 with a white undercrust, and deeply pitted from kaoliniza- 

 Uon of the felspar. Quartz veins, a few inches in width, 

 traverse the exposure in an east and west direction, stand- 

 ing vertically. 



The next exposure to the northwest on the line of the 

 section is 71 feet wide and of the same rock (865) as the 

 last, with rather more felspar, and showing the same 



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s.S" 



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