﻿120 NEW YORK STATE MUSEUM 



zones have been noted in the Paleozoic rocks, and the deforma- 

 tion which gave rise to them seems certainly of Precambric date, 

 though later than that previously described since the rocks were 

 under less load, hence nearer the surface. 



In the Paleozoic rocks. Frequent faults of small throw may be 

 made out in the Potsdam sandstone. The red and white banded 

 stone which constitutes the lower part of the formation on the 

 Alexandria quadrangle is excellently adapted to display them, 

 and a magnificent exhibit of them is given on the bare rock surface 

 of the large Potsdam outlier which lies between the railroad and the 

 north end of Butterfield lake. Here over a considerable area the 

 faults are spaced but a few feet apart, and though the throw seldom 

 amounts to as much as a foot, and is frequently only a fraction of 

 an inch, the combined displacement of the whole must l}e quite con- 

 siderable, as there are hundreds of them. For a hand specimen from 

 this locality, showing one of these faults see plate 31, upper figure. 

 All noted are normal faults of slight hade. The fault planes are 

 filled with sand grains in all respects like those of the rock itself and 

 as thoroughly cemented, which would seem to indicate that the 

 faulting occurred before rock cementation was far advanced, so that 

 the grains gave way individually instead of as sandstone fragments, 

 whereas the latter would certainly be the method were faulting to 

 take place in the rock now. Cementation subsequent to the faulting 

 has thoroughly indurated the whole. 



The bulk of the formation is rather uniformly colored and 

 hence not so well adapted to display faulting of this type, and it 

 is not certain whether it occurs in it or not. 



There are also occasional small faults of a later type in the 

 Potsdam, the fault planes remaining as open cracks, with sand- 

 stone fragments in the fault breccias. A small fault of this type 

 appears in plate 12. 



In the limestones a few faults have been noted whose throw 

 amounts to several feet. The best example seen by the writer 

 is in the lower Pamelia limestones of the Pamelia inface, 2 miles 

 east of Perch lake. The section here shows the basal, black, 

 fossiliferous limestones, overlaid by a thickness of some 15 feet of 

 thin bedded, earthy limestone, followed in its turn by massive 

 blue limestone with interbedded gray magnesian layers. These 

 upper massive limestones are faulted down against the earthy 

 limestone, the fault bearing n. 30 e, downthrowing to the east 

 and with a throw of some 20 feet. 



