REPORT OF THE DIRECTOR I914 



137 



visible only in the Trenton Falls gorge and in the bed of Cincinnati 

 creek i^ miles southwest of Prospect. 



HYPOTHESES REGARDING THE CAUSE OF THE CONTORTIONS 

 Tectonic hypothesis. The explanation offered by the writer is 

 that the contorted zones w^ere produced by differential movements 

 within the mass of the Trenton limestone. The displacement 

 (140 feet) of the thrust fault at Prospect village was sufficient to 

 cause the beds of the middle Trenton to slide over beds of the 

 upper Trenton. Near the fault-surface the strata on the upthrow 

 side are bent upward at angles of from 30 to 40 degrees. Figure 2 

 shows the relation of the folded zones to this fault. 



S CA L C : 

 e 10 



F E C T. 



Fig. 2. Section showing the position of the two corrugated zones within 

 the Trenton formation and their relation to the thrust fault at Prospect, 

 near Trenton Falls 



It is easy to see how, when the force of compression was brought 

 to bear in the region, the higher Trenton beds on the upthrow side 

 must have moved more easily and consequently faster than the 

 lower Trenton beds. For instance, the portion A in figures i and 2 

 being separated from C by an intermediate mass B of possibly 

 slightly less rigidity would slide over C and cause the portion B 

 to become ruffled or folded and fractured. Occasionally parts of 

 zone B would be moved very little or would be moved along with- 

 out being folded. The portion B would need to be only very slightly 

 less rigid than the adjacent portions. The somewhat thinner lime- 

 stone layers separated by thicker shale partings would cause the 

 part B to be thus less rigid. A similar explanation applies to the 

 lower folded zone, and the folded or contorted zones thus merely 

 indicate horizons along which the differential movements have taken 

 place. 



