4.6 NEW YORK STATE MUSEUM 



and mapping of these faults well within the Precambric area. The 

 North Creek quadrangle, which lies in the midst of this eastern 

 Adirondack faulted region, is literally cut to pieces by faults. On 

 the accompanying geologic map the writer has indicated the posi- 

 tions of over forty faults, most of which show unmistakable evi- 

 dences of their presence, while the others, shown on the map by the 

 heavy broken lines, are more or less certainly present. 



The faults are all of the normal type with fault planes vertical 

 or very steep. Because of the character and structure of the rock 

 masses and the lack of any well-defined stratigraphic relations, it 

 is practically impossible to determine the actual amounts of dis- 

 placement, though in many cases minimum approximations can be 

 made. Such minimum figures commonly range from a few hundred 

 to a thousand feet or more. One feature worthy of special mention 

 is the frequent rapid diminution of throw within very short dis- 

 tances. Thus in many respects the North Creek faults are much f 

 like those of the Mohawk and Champlain valleys, which is to be 

 expected as the faults of this whole eastern Adirondack region were 

 all produced at the same time or times. With regard to the strike, 

 however, the North Creek faults are rather exceptional because the 

 general trend of the Adirondack faults is north-northeast by south- 

 southwest, while within the North Creek quadrangle this trend is 

 the rule only in its northern portion. 



As a rule, faults within the Precambric area are difficult to locate 

 and trace with any great degree of accuracy and certainty because 

 of the general similarity of the rocks and the lack of ordinary fos- 

 siliferous strata. In the North Creek region, however, the condi- 

 tions are particularly favorable for locating faults both because of 

 the unusual excellence of exposures and the large amount of widely 

 distributed weak Grenville strata. 



Frequently the line of contact between the syenite or granite and 

 the Grenville is very regular and sharp, the Grenville often seeming 

 to dip under the igneous rock with the latter rising abruptly and 

 to a great height above the Grenville. Among the best examples of 

 such phenomenon are the southern sides of Huckleberry, Crane, and 

 Little mountains, and the western sides of Oven, Prospect, Birch, 

 and Potter mountains. There are only two possible explanations 

 of this phenomenon, namely, either that the igneous rocks were in- 

 truded into the positions which they now occupy or that faulting 

 has occurred. If this is to be explained simply on the basis of in- 

 trusion, then we are forced to assume a remarkably irregular surface 



