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NEW YORK STATE MUSEUM 



in the older stratified formations. They result from strains in the 

 outer zone of fracture and thus are connected with the formation 

 of secondary joints. As already noted, a system of very marked 

 jointing is often accompanied by differential motion of the rocks 

 involved, which is denoted by their polished surfaces. When the 

 displacement is considerable, the rocks along the fracture are much 

 broken and sometimes mashed into a mineral pulp in which much 

 alteration has taken place. 



a 



Fig. I Simple faults. 

 b the reversed fault 



illustrates the common or normal fault, and 



Faulting is most common and of the greatest magnitude in the 

 Adirondack area of which the whole eastern and southeastern 

 boundaries between the upraised and folded crystallines and the 

 horizontal Paleozoic sediments are defined by a series of faults. Like 

 the massive joint systems of that section, they have a northeasterly 

 to northerly trend ; their downthrow is toward the east. Some of 

 the: interior Adirondack valleys are undoubtedly the result of fault- 

 ing, either of single or compound type, but in this case, the evidences 

 of actual displacement are not so apparent since it is confined to 

 the crystallines alone. Valleys with abrupt slopes on both sides may 

 be due to the sinking of the block between two faults, as is thought 

 to be the origin of the Lake George basin. There is need of caution, 

 however, in ascribing the existence of scarps and deep valleys in 

 this region to faulting, as the normal course of weathering and 

 particularly the wear of glacial ice would tend to produce sharp 

 contours along the main joint systems. 



Fig. 2 Normal faulting in inclined strata; the same beds outcrop repeat- 

 edly when traced across the strike 



