REPORT OF THE DIRECTOR AND STATE GEOLOGIST rlOl 



This is on the road running northeast from Alexandria Bay, 

 near the river, and about two miles from the village. In the 

 midst of a flat area of Potsdam the granite-gneiss appears, its 

 sin face level with that of the surrounding sandstone, and like it, 

 well smoothed by glaciation. A quarter of a mile northwest, the 

 Potsdam drops away with an abrupt slope down to the gneiss 

 which stretches along the river. The sandstone is horizontal, 

 and about forty feet thick, so that the granite-gneiss now pro- 

 jects up into it this distance, and has lost an unknown upward ex- 

 tension by erosion. 



All of these facts taken together render it practically certain 

 that the Potsdam was laid down on an uneven surface of the 

 crystalline rocks. 



The same conclusion was drawn by the writer 1 five years ago 

 from study in Gouverneur and Antwerp, but the data then avail- 

 able were much less reliable. Gushing 2 holds the same view for 

 the region studied by him; while Kemp 3 has applied it tentatively 

 to the entire Adirondack region. The writer hesitates to accept 

 the latter generalization till supported by more data than are 

 yet available. 



Some years since, Lawson 4 gave reasons for believing that the 

 Cambrian and Silurian rocks of Canada were also deposited on 

 a rolling surface of crystallines. But Crosby 5 has recently de- 

 scribed the contact of Potsdam and pre-Cambrian rocks in Colo- 

 rado, showing that the former were laid down on a nearly plane 

 surface. From this fact, together with the nature of the sand- 

 stone, he draws some broad generalizations of much interest and 

 importance. 



For the region here under consideration, however, these gen- 

 eralizations do not hold good, since we have a sediment free from 

 arkose and in close proximity to an erosion unconformity, but 

 the unconformity is not, as according to Crosby's hypothesis, it 



x 13th an. rep't N. Y. state geologist. 1893. p. 509. 

 2 0p. cit. p. 6. 



3 Bui. geol. soc. Amer. S:408-12. 

 *md. 1:163-73. 

 b IMd. 10:141-64. 



