﻿Triassic formation of the Connecticut Valley. 349 



one that separates Lamentation Mountain from the Hanging 

 Hills — and if drawn on true scale it cannot be supposed that 

 displacements of so great a measure could fade away within 

 the thickness of the Triassic beds, even if they were ten or fif- 

 teen thousand feet thick. The faults must penetrate to a depth 

 many times greater than their throw ; to a depth commensurate 

 with their length, and this may be five or ten miles. This 

 gives us literally a deeper insight into the Triassic disturbance, 

 and points out another important requisite in the hypothesis 

 for its explanation : the disturbance must affect not only the 

 Triassic rocks, but a broad and deep mass of the earth's crust 

 with them. Attention has been too generally given to the 

 Triassic rocks alone ; it will be well to invert the problem, and 

 look for a time at the underlying schists and gneisses to dis- 

 cover how they may have yielded to a disturbance ; letting the 

 superficial covering of Triassic beds take the consequences of 

 it, and adapt themselves to the dislocation of the surface on 

 which they rest as best they may. 



The fundamental rocks are great slabs of crystalline schists 

 and gneisses, varying strongly in composition and texture. 

 Some are massive and almost granitic ; others are finely foliated. 

 The attitude of the slabs is hardly more constant than their 

 composition ; but they are in general more nearly vertical than 

 horizontal, and their prevailing strike is north or east of north. 

 The Triassic strata were laid down on the edges of these 

 steeply inclined slabs after they had been bevelled off* to a tol- 

 erably even surface by pre-Triassic erosion. The character of 

 the deformation of the schists would depend on the action of 

 the deforming forces. 



The general position of the Triassic areas as well as the de- 

 tail of their structure at once suggests their connection with 

 the Appalachian system of disturbances. The depression of 

 the long trough-like areas in which the Triassic strata accumu- 

 lated as well as the subsequent disturbance of the accumula- 

 tions is most naturally referred to a late manifestation of the 

 forces that had at an earlier date produced the great system of 

 Appalachian folds; and as such should be regarded as the re- 

 sults of a slow, irresistible, horizontal crushing force or com- 

 pression, acting east and west or southeast and northwest. No 

 definite limit can be set to the depth through which the com- 

 pression acted ; but judging by its effects in the writhing and 

 folding of the Appalachian strata, it must have had a profound 

 penetration ; and if the theories that have been suggested to 

 account for the compression may be trusted at all as guides, 

 the thickness of earth's crust affected by it must be measured 

 by tens or even hundreds of miles. 



A group of inclined slabs, compressed by a horizontal force 



Am. Jour. Scl— Third Series, Vol. XXXII, No. 191 —November, 1886. 

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