422 



NEW YORK STATE MUSEUM 



But in the reaction of the region from compression, tension 

 faulting took place on a large scale, and its eastern portion was 

 sliced by the series of meridional faults which cross it. Since 

 these uniformly downthrow to the east, they produced a step- 

 like topography of eastward facing fault scarps, with intervening 

 terrace platforms. In the Champlain region the faults were 

 numerous, and often of large throw, their combined effect being 

 to cause a rapid drop in altitude eastward, and to produce a 

 depressiom along the Ohamplain meridiam. But at the same time 

 the region still further east was uplifted, miainly by folding and 

 thrust faulting, thus outlining the Champlain vailley as a great 

 structural depression, or trough, closely coineiding in position 



Fig. 7 Diagram of a single normal fault to illustrate the local character of the sur- 

 face derangement. The rock layers on the upthrow side are given a dip away from, 

 and those on the downthrow side a dip toward the fault plane, but at the ends of the 

 figure the rocks remain as before the faulting. 



with the previous depression of the Chazy basin. The region 

 directly to the west of this depressed^ strip was^ givea considerable 

 altitude by the general elevation, and it seems likely that it 

 formed then, as now, the most elevated portion, with a rapid step- 

 like drop to th6 east, and a gentle and more even slope toward 

 the west. Passing westward, the faults become much fewer in 

 number, and, while they interrupted the prevailing westerly slope 

 with their scarps, the interruption was but local [fig. 7]. This 

 is well illustrated by the Mobawk valley faults, in whose vicinity 

 a strong increase in the westerly component of the dip is always 

 observable, whiich flattens back to the normal amount with in- 

 creasing distance from the fault. 



In some few cases trough faulting was brought about by a 

 pair of faultsi throwing in opposite directions, and depressing 

 the block between. Between the Little Falls and Dolgeville 



