68 NEW YORK STATE MUSEUM 



to the west, but the north-south direction was chosen in order to 

 avoid the tipping produced by faulting, so far as possible. 



Since the erosion level whose presence is indicated hy the con- 

 cordant hilltop altitudes does not correspond with the older 

 erosion plane on which the Paleozoic rocks rest, but makes an 

 angle with it, it follows that it must have been developed during 

 a later erosion period. It follows further that the more we recede 

 from the present Paleozoic contact line, the more deeply erosion 

 has cut away the pre-Cambrian rocks. 



The area under discussion is so small, and the writer has so 

 little familiarity with the surrounding district, that it would be 

 folly to attempt to trace the erosion level beyond the district, 

 either north or south. That it represents an old level is quite 

 clear, and that it should also be traceable south of the Mohawk i» 

 equally clear. The larger portion of the area of the Little Falls 

 sheet has been cut down by later erosion to a lower level. It 

 should be pointed out, however, that the concordant hilltop alti- 

 tudes, as found here, are also found in the northwestern Adiron- 

 dacks, but are not to be found on the east and northeast, because 

 of which the writer has argued for recent movements along the 

 fault planes in the latter district as a probable reason for their 

 absence ; that is, that the erosion surface was produced there as on 

 the west and south, but that its continuity has been broken by 

 recent differential movements along the old fault planes. 



Present surface of the Paleozoic rocks 

 As the Little Falls district emerged from the sea after the de- 

 position of the Paleozoic rocks, it presented a low and quite 

 smooth surface, with a gentle inclination to the south or south- 

 west. Since at present the rocks are but slightly tilted from their 

 original nearly horizontal attitude, the original uplift, as well 

 as all others since, has affected their inclination but little. The 

 diagram, figure 13, represents a rude attempt to illustrate the 

 structure of the region on emergence, on the assumption that this 

 took place at the close of deposition of the Medina sandstone of 

 the Upper Silurian. This is in all probability not the case, but 



