﻿Triassic formation of the Connecticut Valley. 343 



so wholesale a process, it is excluded first by the occurrence of 

 coarse conglomerates on the eastern margin of the formation 

 where they dip strongly toward the ledges of crystalline rocks 

 from which they were doubtless derived, and from which they 

 are now separated by a well-proved fault, with heavy down- 

 throw on the western side ; second by the numerous faults in 

 the middle area of the formation, whereby the trap-ridges are 

 so systematically repeated. Whatever hypothesis be accepted 

 in explanation of the monoclinal attitude, its first requisite is 

 for these reasons that the strata have actually been disturbed 

 since their deposition. 



It has been more recently proposed * to account for the Tri- 

 assic monoclinal in New Jersey, which in so many ways re- 

 sembles that of the Connecticut Yalley, by a progressive dis- 

 turbance during the deposit of the strata. The mechanical 

 difficulties in the way of this process are to my mind rather 

 formidable, but independently of these, it cannot be accepted 

 for the Connecticut Valley, because it does not account for the 

 occurrence of faults that here form so characteristic a part of 

 the structure and that are so essentially connected with the 

 rest of the deformation. Moreover, before the faulting the 

 strata now disjointed must have been continuous ; and the 

 nearly uniform thickness over large areas of the trap overflows 

 that are buried between the sedimentary beds shows that they 

 at least could not then have been inclined at their present dip, 

 but that the whole series must have lain essentially horizontal. 

 Finally, the displacement of the highest as well as of the lowest 

 members of the series by the faults, and probably in some 

 cases by the same fault, indicates that these dislocations did not 

 begin till after the whole formation was practically completed ; 

 or to put it in a more natural form, this indicates that the 

 period of deposition continued until it was closed by the eleva- 

 tion accompanying the disturbances that have given rise to the 

 existing structure. It is probable, on the other hand, that cer- 

 tain uneven changes of level took place during the accumula- 

 tion of the strata, for they are of considerable thickness on a 

 rather limited area, they present many marks of shallow water 

 during their deposition, and extended eruptive action charac- 

 terized the latter part of the period ; but these changes may 

 practically be neglected in seeking for an explanation of the 

 existing structure. The second requisite of an acceptable 

 hypothesis is therefore that it should recognize the original 

 horizontal position of the beds, and place their disturbance 

 after the accumulation ended. 



The occurrence of igneous rocks so closely associated with 

 the Triassic formation, not only in the Connecticut Valley but 

 *Cook, Geology of New Jersey, 1868, 174. 



