64 NEW YORK STATE MUSEUM 





to curve from the north to the northeast and from the northeast 

 back to the north. It has been shown that there are principal joint 

 sets in both these directions in the region and the fault slips are 

 thought to be determined in position by these joints. The average 

 trend of the faults is to the north-northeast. In this direction there 

 are no main joints. The faults maintain this general direction by 

 alternately following the north and the northeast joints, this appar- 

 ently being a more easy method of accomplishing the deformation 

 with north-northeast trend than the method of creating new frac- 

 tures in that direction along which the slipping might take place. 

 Both the Hoffmans and the McGregor faults illustrate this curving 

 tendency. 



The faults send off frequent branches, which are more likely to 

 appear at a curve. In many cases one branch will be found in a 

 north-south and the other in a northeast-southwest direction. By the 

 branching, the throw of the fault is divided among the branches 

 It often happens that the throw of the branches steadily diminishes 

 until they fade out while at the same time that of the main fault in- 

 creases until it attains the amount it had prior to the branching. 

 This process seems frequently repeated. 



During the successive stages of the faulting in the region, as 

 the long rock slices slipped past one another, it is but natural that 

 irregularities in the slipping would develop, producing cross strains 

 in the slices and tending to promote cross breaks. That such cross 

 breaks are of frequent occurrence in the general region is quite 

 certain, though exposures are not sufficiently good to permit their 

 certain location within the Saratoga quadrangle. The obvious 

 tendency would be for such cross breaks to occur along planes of 

 weakness, such as the contacts between two formations of very 

 different strength. There seem to be two zones in which such 

 breaks would be most apt to occur, one at the contact between the 

 Precambric crystallines and the Potsdam sandstone, and the other 

 at the contact between the limestones and the overlying shales. 



There is some suggestion of frequent cross breaks in the faulted 

 slices at the Precambric-Potsdam contacts, but in no case known 

 to us has the evidence been worked out in detail. A prominent 

 topographic feature of the southeast border of the Adirondacks 

 is the way in which the Precambric portions of the fault slices 

 sharply break down on the south to the level of the Paleozoic plain. 

 In every one of the faulted slices the Precambric rocks are fol- 

 lowed by Paleozoic rocks on the south. The Precambric territory 



I 



