Jura-Trias trap of the New Haven Region. 169 



The conformability of beds in monoclines is usually proved 

 to be a fact by the study of transverse sections. But in the 

 case of the trap and sandstone of the Jura-Trias area of 

 Eastern America, no transverse section exhibiting such con- 

 formability between the trap and sandstone has yet been made 

 known by any observer. 



III. An emergence of the sandstone placing it more or less 

 above the sea-level is necessary to render the method of 

 hydration above appealed to possible. There is other evidence 

 of such emergence. 



The existence of dikes of amygdaloidal trap in East Haven,, 

 and of others of compact anhydrous trap in, New Haven local- 

 ities, two to five miles apart, is evidence, as explained in my 

 Geology, of the hydration of the liquid rock, in the former 

 region while on the way to the surface ; for the lava at its 

 source must have been all alike. This must have taken place 

 during its ascent through the sandstone ; for, as shown by E. S. 

 Dana, the trap of the related dikes that intersect the meta- 

 morphic rocks is unusually anhydrous. The New Haven dikes 

 are situated along the western slope of the Connecticut valley 

 trough, and those of East Haven toward or at its center, 

 where the subterranean waters would have flowed. Hence the 

 difference. But if the sandstone were wholly under the sea- 

 level, the amount of subterranean water could not have thus 

 differed, in the two regions ; and consequently, there was some 

 emergence. 



If the sandstone formation was thus early emerged another 

 conclusion follows. The trap of the Lake Saltonstall and 

 Hartford Range (its more southern part marked EI, EII, EIII 

 on Percival's map) — which I have shown to have originated, 

 in all probability from fissure-ejections subsequently to the 

 upturning of the sandstone — would have made, as I long since 

 explained, a barrier to the Connecticut River waters, that 

 would have cut off their flow southward and determined sooner 

 or later their discharge by the present Middletown- Say brook 

 outlet. (See Percival's map.) These facts therefore bear on 

 Prof. Davis's hypothesis, and on his deductions from it as to 

 denudation over the region of the Connecticut valley. 



