308 BULLETIN OF THE 



large and small trap sheets were forced laterally between the deep-lying 

 strata. The period of deposition, and probably of eruption, was ended 

 by an uplift that drained the sandstone areas, and tilted the included 

 strata by small amounts from their original position. Some of the strips 

 were bent into simple or faulted synclinals (Nova Scotia, Richmond coal 

 field) ; one was thrown into gentle waves (Prince Edward Island) ; the 

 others received their peculiar raonoclinal tilting. Why the general 

 monoclinal structure was produced cannot now be clearly explained ; 

 but by means of the overflow trap sheets, which serve perfectly as iden- 

 tifiable horizons in the monotonous sandstones and shales, it can be 

 shown that there are distinct folds in these monoclinals, thus explaining 

 the crescentic form of the trap ridges. The folds are of small pattern 

 in Southern Connecticut; on a much larger scale in Nova Scotia, Massa- 

 chusetts, and New Jersey. Faults also occur : some of small throw are 

 directly visible ; some of much greater displacement are properly inferred 

 from the repetition of similar series of strata ; and many more probably 

 exist hidden under drift and soil : thus the necessity is avoided of sup- 

 posing a great thickness for the formation. The erosion of the sedimen- 

 tary and igneous strata into their present form was probably accomplished 

 in great part during a time of greater land elevation than the present ; 

 but it presents nothing abnormal. 



The physical features of the Triassic belts that seem most worthy of 

 further observation are, first, a closer identification than has yet been 

 made of the source of the conglomerates that not unfrequently occur 

 along either margin of the belts, thus allowing or excluding the ideas of 

 original oblique bedding and of anticlinal remnants ; second, the deter- 

 mination of the overflow or intrusive origin of the many undetermined 

 trap ridges ; third, the further proof that the curvature of these ridges 

 implies a folding of the strata ; fourth, the closer identification of the 

 surmised but undiscovered faults. 



Cambridge, January 8, 1883. 



