2/6 NEW YORK STATE MUSEUM 



Amount of displacement. The greatest throw noted on anv 

 single Postglacial fault in eastern Xew York is given by Wood- 

 worth as 6 inches, and he remarks that this is imperfectly shown. 

 Usually the displacement is distributed over a zone in which several 

 small faults occur instead of a single larger one. This may mean 

 that the whole disturbance is essentially superficial. 



At South Troy it is stated that a total displacement of 12 inches 

 is thus distributed through a number of small faults within a dis- 

 tance of 30 feet. 



At Rensselaer a total of 5 inches is given. 



At Defreestville a total of 13 inches is indicated in a distance 

 of 11.67 fest. 



At Copake, at two different spots, a total of more than 7 inches 

 was measured within a space of 12 feet. Woodwortli thinks that 

 the total displacement for the locality may exceed 2 feet. 



At Pumpkin Hollow a total of 17 inches is estimated. 



Conclusion. If such rates prevail over larger areas beneath 

 the drift, it is clear that rather profound changes would be indi- 

 cated. But thus far there is no indication of such continuity. 



Likewise if it were certain that the movements are now in 

 progress, it would be a matter of greater concern. But there is 

 no direct evidence to prove it. 



Estimiates of the length of postglacial time differ greatly. The 

 shortest ones worthy of consideration range from about 5000 to 

 10,000; the longest run above 100,000 years. 



Some intermediate value is probably nearer the truth — say 

 25,000 years. 



Adjusting the postglacial faulting problem then to these time 

 estimates the summary of it all would be as follows : Somewhere 

 within postglacial time, i. e. approximately 25,000 years, move- 

 ments of strata have developed at a few places in eastern New 

 York that appear as small faults with total throw in each locality 

 varying from a few inches to perhaps as much as 2 feet. Whether 

 the movement has been gradual and continuous or concentrated 

 largely into s6me small portion of this time is not known. Whether 

 the effects are extensive or, on the contrary, very local and super- 

 ficial, is likewise unknown. But in any case there are no known 

 instances of violent and large displacements, such as would be 

 likely to cause great damage to sound structures, in this region in 

 postglacial time. 



