430 NEW YORK STATE MUSEUM 



greatly uplifted as compared with it, that to the west considerably 

 less so. Its own hilltops reach concordant levels, and probably 

 represent the Cretaceous base level, but dropped below its normal 

 altitude. 



Faults as topographic features 



As has been stated, it is probable that all fault scarps in the 

 region disappeared by being worn down during the Cretaceous 

 base-leveling period. Such wearing down customarily brings 

 different rock masses into juxtaposition on opposite sides of a 

 fault. Any renewed uplifting of the district then tendst to cause 

 a reappearance of a scarp along the fault line, owing to the more 

 rapid wearing away of the weaker of the two rocks. The hight 

 that this scarp may attain will have the difference between the 

 old and the new base levels for lits maximum value, and the 

 proportion of this actually attained will, other things being 

 equal, depend on the comparative resistances of the two rocks. 

 If one is very strong and the other very weak, relative promi- 

 nence may be gained, specially in the near vicinity of drainage 

 lines. The weaker rock may be on either the downthrow or the 

 upthrow side, and, according as the first or the second is the 

 case, the scarp will face in its original, or in the opposite direc- 

 tion, in the latter case giving rise to the anomaly of the down- 

 throw side standing at a higher level than the upthrow. In the 

 cases where there is little or no difference in resistance between 

 the rocks on the two sides, there will be no tendency to cause 

 reappearance of a scarp along the fault line. 



Furthermore, except in the case of faults which exactly 

 parallel the strike, the surface rock will vary from time to time 

 on the same side of the fault, and with these changes, now on 

 one side and now on the other, the iscarp becomes either less or 

 more pronounced than it wais before, as the variation diminishes 

 or increases the difference in resistance of the rocks. In the 

 case of dip faults an irregular topography is sure to be produced 

 along the fault, owing to the more frequent paissage from one 

 sort of rock to another. 



In general, the faults of northern New York show a weaker 

 rock on the downthrow side and hence tend, on uplift, to re- 

 produce a scarp facing in the direction of the original one. 



