40 NEW YORK STATE MUSEUM 



Because of the deep mantle of sand and gravel which now covers 

 the Precambric surface east of Black river, the configuration of that 

 surface can not be studied to the best advantage. But so far as 

 can be judged, if the stream channels in the Precambric surface 

 were filled up the resulting surface would be comparatively smooth 

 and even which strongly argues for that sort of a surface before the 

 stripping ofif of the sediments and later erosion. Any prominent 

 elevations on the old floor ought now to be recognizable, especially in 

 the valley bottom, and near the Paleozoic boundary, but none occur 

 there. The distinct rock ridge southeast of Fowlersville seems to 

 be the only example of such an elevation. This ridge rises about 

 80 feet above the general level but its hight is thought to have been 

 somewhat accentuated by ice action. Again, if there had been any 

 marked depressions in the old floor they would have been filled 

 up with Paleozoic sediments and we might well expect to find such- 

 protected sediments as isolated patches or outliers within the gen- 

 eral Precambric area as, indeed, the Potsdam sandstone does occur 

 some 30 or 40 miles farther northward. The available evidence, 

 however, points to a complete removal of the sediments. 



The conclusion for the Port Leyden quadrangle is that the Pre- 

 cambric floor upon which the sediments were laid down was com- 

 paratively smooth and even, with only one known elevation rising 

 above the general level. This is substantially the conclusion reached 

 by Professor Gushing and the writer for the Little Falls and Rem- 

 sen quadrangles respectively and it is true of the southern and south- 

 western border of the Adirondacks. This result as Gushing says 

 "seems specially important in view of the fact that Professors 

 Kemp and Smyth, and the writer (Gushing) also, have found evi- 

 dence to show that, in the St Lawrence and Ghamplain valleys and 

 vicinity, the surface on which the Potsdam was deposited was con- 

 siderably more uneven than this. In other words, the surface to 

 the south was worn down to a nearer approach to base level than 

 was the case farther north." 



Slope of the Precambric surface where now exposed 



We have just shown that the Paleozoic sediments were deposited 

 upon a very smooth Precambric surface. The uneven and dissected 

 character of that surface where now exposed is due almost entirely 

 to erosion since the stripping away of the sediments. A fairly good 

 idea of the present general slope of this surface may be obtained 

 by comparing altitudes at various points. 



