GEOLOGY OF THE NORTHERN ADIRONDACK REGION 



403 



which produced the greater folds to the eastward. So far as 

 observed, the folds trend nearly north and south. Minor fold- 

 ing, of sometimes considerable amount, ia often observed in the 

 near vicinity of faults, and in many cases at least is a result of 

 the faulting, being apparently due to differential movement 

 along the fault plane. 1 Such folds are small and rapidly die out 

 with recession from the fault plane. 



Westward, along both the north and the south sides of the 

 region, evidence of folding is progressively less evident. That 

 there are low undulations of the strata can not be doubted, but 

 such are found dn nearly all districts, of even the least disturbed 

 rocks, and can be located only with the most painstaking care, 

 if at all. Slight local folds, sags is a better term, are not un- 

 common in the limestones of the Mohawk valley, but seem to 

 be local and not regional structures. 



Faults 



Precambric faulting. The location and tracing out of faults 

 in the Adirondack Precambric is an exceedingly difficult task, 

 and, in so far as they have been located, their recognition has 

 depended more on topographic than on structural evidence. 

 The discrimination between Precambric and later faulting is 

 trebly difficult, and for the most part has not been attempted. 

 Practically all topographic indications of Precambric faults 

 must have been obliterated during the protracted period of Pre- 

 potsdam wear on the then land surface of the region. At the 

 present day large faults of the sort could be most readily de- 

 tected at the Precambric margin, by showing that the over- 

 lying sediments had not been affected by the process. No such 

 evidence has yet been forthcoming so far as the writer is aw T are. 

 Yet there does seem to be evidence of at least some Precambric 

 faulting. 



In the eastern Adirondacks, where diabase dikes abound, it 

 is a frequent experience to find them faulted. Often the same 

 dike will be faulted more than once within comparatively small 

 distance. The recognizable faults of this sort are usually of very 



*Folds of this sort are shown on most of Brainard and Seeley's excellent 

 sketch maps of bits of the Champlain region. See for example Am. Mus. 

 Nat. Hist. Bui. 8:301Kll. and Am. Geol., November 1888. p.32fi. 



