1882.] 123 [Davis. 



It is noticeable that the throw of the large fault is in the direc- 

 tion to increase the breadth of country occupied by a given set 

 of strata ; and thus to reduce the estimate of the thickness of the 

 sandstones demanded by the simple monoclinal tilting without 

 faults ; such faulting is therefore a very economical modification 

 of the Hitchcock-Leconte supposition. 



While the faults are indicated by the repetition of the trap 

 outcrops, the gentle folds or waves are fully proven by the curved 

 outline of the ridges, and by the complete conformity of the ad- 

 joining sandstones to their curving. But the occurrence of these 

 folds has been generally denied, and the explanation of the sup- 

 posed monoclinal greatly retarded by an assumption of regularity 

 in the strike and dip of the sandstones, that does not exist. The 

 curved or crescentic form of the ridges shown by Percival in 

 1842 to be constant in each belt and to have a constant relation 

 to the dip of the sandstones, has generally been taken as mark- 

 ing a curved fissure up through which the trap has been ejected. 

 Bat such explanations completely fail to explain the overflow trap 

 sheets which are shown to be essentially interbedded members of the 

 Triassic series, and which have consequently suffered just the 

 same distortion as their enclosing sandstones and shales. In order 

 that an originally flat sheet shall have a curved outcrop, it must 

 be folded ; and conversely, if folded, it must have a curved out- 

 crop. In this simple way, therefore, the puzzling crescents may 

 be explained. The fact that the crescents of the Connecticut 

 area are all convex westward is the result of their folds taking 

 part in the general monoclinal structure, and canting over a little 

 to the eastward ; and also because these folds are often faulted 

 up to a second appearance in another fold on their eastern side. 



One fact of capital importance remains unexplained. We 

 may admit that the Connecticut strip of sandstones is not greatly 

 reduced from its original area ; that its dip is not the result of 

 oblique deposition, but of post-Triassic disturbance; that most of 

 the trap ridges are the edges of contemporaneous overflows of 

 lava ; that their curvature and their occasional reappearance are 

 the results of folding and faulting which they suffered with the 

 sandstones ; but there has as yet been no satisfactory reason as- 

 signed for their general monoclinal structure. This most strik- 

 ing physical feature of the Triassic belts is still a mystery. 



