232 



THE POPULAR SCIENCE MONTHLY. 



tion is unconformably overlain by the Cretaceous strata of the 

 coastal plain, proving that the sandstones were not only tilted but 

 deeply eroded before the Cretaceous beds were laid upon them. 

 The formations in New Jersey and Connecticut are so much alike 

 that we may safely conclude that the period of dislocation was 

 the same in both ; hence we shall suppose that the Meriden sand- 

 stones and lava-sheets were tilted and faulted into the position 

 illustrated in Fig. 10 during the interval between Triassic and 

 Cretaceous time — that is, in the Jurassic period. From that time 

 to now their history is concerned chiefly with the erosion by 

 which their original constructional inclined planes have been re- 

 duced to their present surface of varied topography. 



There is good reason to think that the history of the erosion is 

 a double one, comprehending first a longer cycle, and second a 

 shorter cycle of time. During the first cycle, the great relief of 

 the uptilted beds was reduced to a lowland of denudation, a sur- 

 face of a moderate relief close to the base-level of erosion, an 

 almost i^lane surface, a " peneplain " — the evidence of this being 

 found in the even uplands of the crystalline plateaus which now 

 inclose the Triassic valley on the east and west. No explanation 

 for the evenness of these plateaus can be found save the one which 

 regards them as having been reduced from some greater mass by 

 a long-continued process of erosion, at a time when the region 



stood somewhat low- 

 er than now — low 

 enough to place the 

 present plateau-like 

 uplands close to sea- 

 level ; and the sand- 

 stones, shales, and 

 lava-sheets between 

 the two j)lateaus un- 

 doubtedly suffered 

 the same denuda- 

 tion. This is indi- 

 cated in Fig. 11, in 

 which all the ui:»per 

 part of the model as 

 shown in Fig. 10 has 

 been removed; the obliquely beveled surface of the beds now rep- 

 resents the lowland of denudation, or peneplain, to which they were 

 reduced. The effect of the oblique faulting is now rendered appar- 

 ent by the dislocations in the belts of the different outcrops. The 

 main sheet of lava, for example, is seen in each of the blocks into 

 which the formation is divided by the faults ; so is the belt of 

 shales lying under it, and so on with every member of the series. 



Fig. 11. 



