THE GEOLOGICAL HISTORY OF NEW YORK STATE WS 
valley. To a considerable degree the topography of the valley is 
affected by the faults, especially where the harder Precambric or 
Cambric rocks form the scarp or upthrow sides of the faults. This 
is particularly true at Little Falls and the “ Noses” (near Yosts) 
where, in each case, the Mohawk river has cut a gorge across a 
prominent fault scarp and even down to the underlying Precambric 
rock which has been brought relatively nearer the surface by the 
tilting of the earth blocks (see figure 7). On the geologic map of 
the State (figure 1) two tongues of Paleozoic rock are seen to 
extend northward well into the Precambric rock area, and these are 
to be explained by the fact that, due to faulting along the west 
sides, the Paleozoic strata, for fifteen or twenty miles, have dropped 
down (relatively) fully 1500 feet with respect to the Precambric 
rock. The much more resistant Precambric rock has stood out 
against erosion and in each case rises with steep front from 1000 
to 1500 feet above the Paleozoic rock surface (see figure 26). The 
small remnant of Paleozoic strata already referred to at Wells in 
Hamilton county was dropped down fully 2000 feet by faulting 
against the Precambric rock just west, and thus this remarkable 
Paleozoic outlier has been preserved from complete removal by 
erosion. 
What is the age of the faulting or, in other words, when were 
-these fractures developed? That some faulting, at least, occurred 
during Precambric time has been well established but, so far as 
known, those faults are of very minor importance, certainly having 
no appreciable influence upon the existing topography, 
During the Paleozoic era, however, there is good reason to think 
that considerable faulting took place. At just what time during the 
era the faulting occurred is not now altogether certain, but it is 
certain that it was sometime after the deposition of the Ordovicic 
sediments because at many places those rocks are involved in the 
faulting. Cushing has suggested that the faulting may have been 
initiated at the time of the Taconic revolution when the rocks of 
the region immediately eastward were so greatly disturbed, but he 
says, “the great earth disturbances (Appalachian revolution) which 
prevailed in the Appalachian zone toward the close of the Paleozoic 
would seem more likely to have brought about the major faulting 
of the reigon.”* At this latter time the rocks of northern New 
York were not folded but, as we have learned, the whole State was 
notably elevated, and during this disturbance conditions were cer- 
IN. Y. State Mus. Bul. 95, p. 405. 
