138 NEW YORK STATE MUSEUM 



Some of the points favoring this tectonic hypothesis are as fol- 

 lows : 



1 The very existence of the thrust fault at Prospect and the 

 distinct folds in the Trenton formation just to the south make it 

 certain that there must have been differential movements within the 

 mass of the formation. 



2 Contorted zones are known to have been produced by differ- 

 ential movement of more resistant beds over weaker beds in various 

 regions of folded rocks (for example, Marquette district of 

 Michigan). 



3 The parallelism of the strike of the folds of the Trenton 

 formation with that of the fault at Prospect. 



4 The parallelism of the strikes of the small folds and faults 

 of the contorted zones with the strikes of the larger folds and 

 the fault at Prospect. 



5 The limitation of the contorted zones to the upthrow side of 

 the only considerable thrust fault in the Paleozoic rocks of central 

 New York. 



6 The absolute limitation of the contorted zones to two very 

 definite horizons in the Trenton formation instead of there being 

 masses of disturbed strata irregularly distributed through the 

 formation. 



7 The worn character of the upper and lower surfaces of the 

 contorted zones marked by layers of limestone sharply broken across 

 and the presence of numerous fragments of limestone. 



8 The corrugations could not have been produced before deposi- 

 tion of the overlying masses because (a) the limestone layers at 

 least were comparatively hard and brittle when contorted, as shown 

 by the numerous sharp breaks; (b) there is no evidence of very 

 irregular or crumpled upper surfaces of the contorted zones with 

 sediment deposited in the irregularities or depressions; and (c) any 

 attempt- to explain the contortions as due to slumping of masses 

 on the sea bottom is utterly opposed by the low angle and direction 

 of slope of the sea bottom as brought out below, and the remarkable 

 thinness and considerable extent (2 miles) of the contorted zones. 



9 Experimental evidence clearly suggests the possibility of pro- 

 duction of contorted zones by such differential movements. 



Hypothesis of submarine gliding. According to Hahn, the con- 

 torted zones at Trenton Falls are excellent examples of phenomena 

 which have been produced by sliding or slumping of masses on a 

 sloping sea bottom during the process of sedimentation. The ac- 

 companying diagram (figure 3) will serve to illustrate the principle. 



