554 NEW YORK STATE MUSEUM 



I. P. Bishop (33) found the facts gathered by him in regard to the 

 limestone belts in Columbia county '^suggestive of a synclinal 

 having the Trenton limestone outcropping on both sides, and 

 with the edge pushed over westward." As a synclinal is only 

 the complement of an anticlinal, these observations prove the 

 overfolded character of the eastern Hudson valley region directly 

 south of the investigated area. That the Taconic mountain, 

 range to the east of our territory is built after the Appalachian 

 type has been demonstrated by I. E. Wolff (45) in an elaborate 

 paper in which it is shown that the Hoosac mountain is an anti- 

 cline. ''This anticline preserves the rocks in their normal posi- 

 tion on the east side, but on the west they are folded under in 

 inverse position with eastern dip."^ 



Fig. 1 Geologic profile of Hoosac mountain. After I. E Wolff. (45 pi. 6, 5a) 



With the presence of folds of Appalachian type to the soiitb 

 and east of our region, the assumption of an anticlinal with 

 underturned west sides to explain the inversion of the zones,, 

 does not seem to be hazardous. 



It was long ago proved by the Professors Bogers (2) that the 

 great faults in southwestern Virginia lie in the direction of axes 

 of plications instead of in monoclinal strata and "coincide in the 

 great majority of instances with the steep or inverted sides of 

 the flexures." It has been farther demonstrated that overfolds- 

 often change into overthrusts, and theoretically should do so, as 

 soon as the differential stress of the layers reaches their ultimate 

 strength (see the lucid exposition of these relations by O. R. Van 

 Hise, 52). The wonderful regularity with which these over- 

 thrust faults appear in the steep western sides of the numerous 

 folds of the Appalachian mountain system has been fully de- 

 monstrated by Bailey Willis (43). 



^One of the profiles has been copied to illustrate this type of raountairk- 

 structure. {See fig. 1) 



