GEOLOGY OF THE NORTHERN ADIRONDACK REGION 



431 



There are however numerous cases where the resistance is practi- 

 cally uniform on both sides. 



In the Mohawk valley region there is no evidence of any recent 

 faulting. The faults are quite typical dip faults, in a district of 

 low dip. Since the Paleozoic rocks there, from the Beekman- 

 town to the Utica, are progressively weaker upward and are all 

 weaker than the underlying Precambric, it necessarily follows 

 that the faults everywhere show weaker rock on the downthrow 

 side, except where the same formation occurs on both. Owing 

 to the recent uplift of the region, the scarps are coming into 

 prominence, specially where they are crossed by streams. In 

 fact, the utter independence of the faults shown by the streams 

 here, is one of the strong arguments against any recent move- 

 ment along the fault planes, and for such present day promi- 

 nence as they have being wholly due to the recent uplift of the 

 region. 



Along the Mohawk the faults show great cliffs facing east- 

 ward, the valley widely opened in the weak shales on the down- 

 throw side, while constricted and gorgelike in the resistant 

 Beekmantown or Precambric rocks on the other. Receding 

 from the river, their prominence is at once lost, and the scarp is 

 either not manifest or but feebly marked. Thus the Little Falls 

 fault, a very noted topographic feature at the river crossing, 

 loses this character entirely a short distance south of it and has 

 no great prominence on the north, when the great difference in 

 resistance of the rocks is taken into consideration. Eventually 

 it passes wholly into Precambric territory and can be no 

 longer traced. While this may be because of the dying out of 

 the fault, there is no evidence that this is the case. If, on the 

 south side, the fault could be followed through the Utica shale 

 belt to where the more resistant overlying rocks appear, these 

 would come in first on the downthrow side, with production of 

 a scarp facing west. 



In the Paleozoic limestones along Lake Champlain, which have 

 great thickness, but no marked difference in strength, the fault 

 scarps are in no way conspicuous at the present day; in fact, at 

 low altitudes there are none at all. At higher levels, however, 

 they appear. Thus the Tracy brook fault shows no scarp in that 

 part of its course shown on the map [pi. 12]. notwithstanding it 



