MUSEUM OF COMPARATIVE ZOOLOGY. 



305 



Conn. (D) ; and a similar one, but of much larger throw, very likely 

 occurs west of Lamentation Mountain, Conn., with uplift on the east, 

 so tliat the trap sheets seen in Lamentation and m the Hanging Hills 

 are really parts of a single overflow. The evidence of this is the repe- 

 tition of similar series of strata as described by Percival in the outcrop 

 fiices of the two mountains ; in each there is sandstone at the base, then 

 the amygdaloid of the anterior ridge, next a limestone at the bottom of a 

 shale, and finally the heavy trap of the ridge line. As shown in fig. 43, 

 the fault is about three thousand feet. It is obvious that a great sav- 

 ing is thus made in the thickness of the sandstone : a moderate depth 

 of formation is made to cover a good breadth of country by its repeated 

 rising to the surface ; the layers do double dnty^, and the vast thickness 

 supposed necessary on the monoclinal theory may be much reduced for 

 Connecticut at least. Similar evidence makes it very probable that the 

 same sheet of trap is repeated by faulting and folding southward from 

 Lamentation Mountain in all the high ridges to that of Saltonstall Lake ; 

 but further observation is needed on this point. 



We have already stated that the uniformity of dip in direction and 

 amount has been exaggerated, especially by H. D. Rogers, who wrote 

 that in the Connecticut valley there is "only one direction of the dip," 

 and in New Jersey, Pennsylvania, and Virginia, " without exception the 

 strata dip in only one direction" {g, 1Q>1; also G70). It was thus that 

 he was forced to prefer the theory of original oblique deposition. But 

 this artificial constraint vanishes when we recognize that fiat folds with 

 faults are perfectly indicated by the curved outlines of the trap ridges, 

 and by the conformity of the sandstones to these curves; for the trap 

 sheets that are shown to be overflows at once take the important position 

 of distinct horizons in the monotonous sandstones and shales, by which 

 distortion can easily be recognized ; just as the scalloped line of outcrop 

 of the Medina sandstone reveals the folded structure of the Appalachians 

 in Pennsylvania, 



The conformity of the sandstones to the curved trap ridges is well 

 known, but has never received its proper explanation. Percival de- 

 scribed the trap ridges as "arranged according to a peculiar system, 

 conformably with which the secondary rocks are themselves arranged" 

 (10). "Tlie trap ranges .... conform, in their arrangement, to that of 

 the sandstone, and indeed have apparently exercised a controlling influ- 

 ence on the arrangement of the latter, thus indicating a cotemporary 

 origin" (321 ; also 299, 408). He further says that both the general 

 and particular direction of strike of the sandstone strata agrees with the 



VOL. VII. — KG. 9. 



20 



