GEOLOGY OF THE VICINITY OF LITTLE FALLS 13 



the first faulting of ithe region took place at the close of the 

 Lower Silurian coincidently with the Taconic disturbance. But, 

 even so, a fault once formed constitutes a line of weakness, along 

 which further faulting is likely to occur whenever the region ex- 

 periences further disturbance. It is by no means unlikely that 

 repeated slips have taken place along the fault planes since they 

 were first formed. 



Two such faults, the Little Falls and the Dolgeville faults, are 

 found within the limits of the map, and thence eastwardly faults 

 cross the Mohawk valley repeatedly. The Little Falls break is the 

 most westerly one which has been detected in the State so far 

 as the writer is aware, though it is not at all unlikely that small 

 ones, at least, will be brought to light farther west. The Little 

 Falls fault has a throw of nearly or quite 800 feet at Little Falls, 

 and is hence of very respectable magnitude. There is another 

 fault on lower East Canada creek, just beyond the map limits to 

 the east. 



The Little Falls district has been nearly or quite continuously 

 above sea level for a long time; since Devonian time in all prob- 

 ability and likely during a part .of the Devonian also. The length 

 of this period of time in years can be measured by no one with 

 any degree of exactness, but a few million years are involved be- 

 yond any question, and quite likely a good many million. During 

 this time its surface has been undergoing wear instead of receiv- 

 ing deposit. A considerable thickness of the rocks which mantled 

 the surface as it rose above the sea has since disappeared, and the 

 present surface rocks are such because of the removal of What 

 originally lay above. Undoubtedly the shales of the Utica 'for- 

 mation once covered the entire area. They have now disappeared 

 from more than half of it. The Trenton has also been worn away 

 from much of the surface, so has the Beekmantown, and the old 

 floor of all these rocks has been eaten away somewhat in the locali- 

 ties where it is now exposed at the surface. Such later formations 

 as may have been deposited have been wholly removed. We can 

 imagine them as replaced in their old position, since we know 

 their order and thickness from their outcrops to the south, but 



