Triassic Formation of the Connecticut Valley. 429 



of shales or sandstones, instead of hard sheets of lava, presuma r 

 bly allowed erosion to follow displacement rapidly, but it 

 seems highly probable that the topography of the region was 

 for a considerable time closely consequent on the deformations 

 that closed the period of deposition and ushered in the long 

 cycle of erosion that has since then endured with little inter- 

 ruption. 



As time went on and the forces of deformation slackened, 

 the forces of erosion made better headway in reducing the 

 region to a water-sculptured topography ; we find existing 

 illustration of this stage of the history of central Connecticut, 

 in the present form of the central ranges of the Great Basin. 

 The following description is also condensed from accounts by 

 Russell. 



The central ranges of the Great Basin are structurally com- 

 posed of long narrow blocks of bedded, aqueous and igneous 

 rocks separated by faults and tilted into monoclinal attitudes ; 

 but the simple original structural form that they may once 

 have had is now no longer immediately apparent ; the oro- 

 graphic blocks here have been long enough exposed to denuda- 

 tion to reduce them to a water-sculptured form, in which the 

 slopes are trenched by numerous ravines, and the ridges are 

 notched by passes which break the crest-line into peaks, and 

 everywhere develop topographic detail dependent on the un- 

 equal hardness of the bedded components of the mass. Much 

 of the detritus taken from the upper portions is now lodged 

 in the depressions between the adjacent ranges. Variety of 

 form has thus been gained, and a marked feature of this 

 variety is that it all tends to the better collection and discharge 

 of .the rain that falls upon the ranges. The topographic 

 variety is now near its fullest development, and with further 

 denudation it must lose strength ; the ravines will consume 

 more of the mass, the passes will be lowered and the peaks 

 will be attacked and reduced from all sides. The original 

 structural form will be then even less distinct than now, and 

 a continually closer approach will be made to the ultimate 

 featureless base-level lowland, to which all land forms are in 

 time reduced, if no disturbance, such as elevation, interrupt 

 the normal simple progress of their geographic evolution. 



Some mountainous variety of form must in a similar manner 

 have obtained for a time in central Connecticut and Massa- 

 chusetts, when the strongly faulted monoclinal blocks were 

 laterally furrowed by ravines and notched by passes. This 

 may be provisionally called the Jurassic stage of the evolution 

 of our district. But even mountainous ridges are not perma- 

 nent. Given time enough, and the faulted ridges of Connecti- 

 cut must be reduced to a low base-level plain. I believe that 



