﻿350 



W. M. Davis — Structure of the 



about at right angles to their strike, might yield in part by 

 minute internal rearrangement, and in part by slipping on their 

 divisional surfaces, so as to reduce their breadth by standing 

 more nearly vertical, that is, more nearly at right angles to the 

 compressing force. In so doing, the upper surface of the 

 group would be somewhat elevated, and at the same time the 

 bevelled edge of every slab would be tilted over by a tolerably 

 constant angle in one direction, and separated from the neigh- 

 boring slabs by a dislocation with the uplift on the side of the 

 direction of dip. In case the compression varied at different 

 depths, diminishing downwards, a shearing force would be 

 introduced, by which the slabs could be thrown over past the 

 vertical. It seems as if some such mechanism as this might 

 account for the faulted monoclinal structure of the overlying 

 Triassic strata, which must follow its hidden action. 



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Figs. 2 and 3. — Hypothetical sections to illustrate the relation of the Triassic 

 strata to the schists which they overlie unconformable. The dikes that supply 

 the intrusive and overflow sheets of trap are drawn in assumed positions; the 

 simplicity of the attitude of the schists is without doubt much exaggerated. 

 When the breadth of the section in the first figure is reduced by a compression 

 that reaches to a much greater depth than the sections include, the slabs of schist 

 slip on one another so as to take more nearly vertical positions, and the overlying 

 beds are thereby broken into blocks and canted over into a monoclinal attitude, 

 with a dip equal to the change in the inclination of the schists ; the faults between 

 the blocks have their upthrow constantly on the east. It is not desired to affirm 

 that the fault planes are in continuation of the foliation of the schists. The hade 

 of the faults has not been determined. 



It is difficult to consider all the natural possibilities of such a 

 process. The number and closeness of the faults would depend 

 on the texture of the schists : the more numerous and closer 



