﻿Triassic formation of the Connecticut Yalley. 351 



the faults, the less would their throw generally be. A change 

 in the number and throw of the faults along their strike would 

 warp the upper surface into flat, dish-like corrugations. 



According to this hypothesis, the fissures which divide the 

 Triassic strata into long, relatively narrow blocks are to be 

 regarded as determined by the divisional surfaces between 

 the slabs of the underlying schists ; as such, the direction of 

 the Triassic faults should correspond with the strike of the 

 underlying schists. This must be the explanation of the 

 oblique, north-northeast direction of the topographic outlines 

 from Hartford to the Sound : for Percival's map shows a broad 

 belt of schists, with strike about north-northeast, approaching 

 and running under the Triassic area at its southwestern margin 

 near New Haven, directly towards the Hanging Hills, where 

 the obliquity of the fractures between the trap ridges is so well 

 seen ; continuing nearly in the same direction, the eastern 

 margin of the Triassic area is found bordered by schists with 

 similar strike, from Glastonbury to Stafford.* The strike of 

 the buried schists determines the strike of the surface struc- 

 ture and topography ; and as the correspondence of these two 

 apparently independent elements was first noticed after the 

 reason for it came to mind, it seemed to me a valuable con- 

 firmation of the hypothesis here presented. Nearly all the 

 ridges of this southern district overlap in advancing order, be- 

 cause the faults, with upthrow on the east, here trend a little 

 to the right of the strike of the trap-sheets, with dip to the 

 east. Where the overlap is receding, it is because the ridges 

 have curved so far to the east that the faults run to the left of 

 their strike, as in Berlin and southern Wethersfield, or on the 

 northern hooks of the Pond and Toket crescents. There is 

 also a necessary correlation between the throw of a fault and 

 the amount of overlap and offset that it will produce : the 

 fault between the Hanging Hills and Lamentation Mountain 

 has probably the greatest throw of any yet found, and the 

 greatest overlap and offset is found between the same ridges. 

 The unique topographic details of the district thus find a sim- 

 ple explanation in the structure that results directly from a 

 single process of mechanical disturbance. 



The receding order of overlap in the range of the Barndoor 

 Hills of Grranby and Simsbury offered opportunity of making 

 further test of the correspondence between the strike of the 

 schists and the trend of the faults and the resulting displace- 

 ment of the ridges. Between Simsbury and Canton, the range 

 bears north and south ; the underlying and neighboring schists 

 should therefore run west of north, so that their strike shall be 



*Percival noticed this alignment, but doubted the continuity of the schists 

 across the Triassic depression. Geol. Conn., 222, 289, 290. 



