MUSEUM OF COMPARATIVE ZOOLOGY. 283 



Origin and Deposition of the Triassic Strata. — There seems to be no 

 sufRcient reason to look upon these stratified deposits as very abnormal 

 in their origin. Their material was derived from the highlands adjoin- 

 ing either side of their estuaries of lakes of deposit, and whatever the 

 agent of importation — glaciers, streams, waves, or tides — the layers 

 were probably coarser along the shores, finer in mid-water, and all essen- 

 tially horizontal when deposited. It is noteworthy that those who look 

 on the present dip as the result of original oblique deposition took this 

 ground less from direct evidence in favor of anything so extraordinary, 

 than from the hope of escaping from what seemed a greater difficulty ; 

 namely, the tilting to a (supposed) constant dip in one direction in each 

 monoclinal belt. 



In addition to the gi-eat improbability of the theory of oblique depo- 

 sition, and its mechanical difficulties -of one sort and another, it has 

 to explain why very nearly all the detritus should have been derived 

 from only one side of each estuarj' ; and this in the face of the frequent 

 occurrence of heavy conglomerates of local derivation on the other 

 side. With the coarse material in the conglomerates, there must have 

 been introduced a great quantity of finer detritus, which was carried 

 farther from shore : how could this have been deposited dipping so uni- 

 formly towards its origin 1 The general absence of conglomerates along 

 the outcrop sides of the estuaries, appealed to by Russell (c, 231-238, 

 251) as evidence of open water and not of shore line there, is partly and 

 perhaps sufficiently explained by the fact that the outcrop side must 

 have lost a large share of its original mass on account of its elevation 

 and erosion. But it should be remembered that conglomerates or coarse 

 sandstones of local origin do occur on the outcrop sides of the belts. 

 Such are mentioned by Percival (430), Cook (b, 336; c, 31, 34), H. D. 

 Rogers (g, 669, 677, 679, 760), and Ken- (b, 141). An example of peb- 

 bles found on one side of a Triassic belt and derived from the other, 

 is given by Wurtz (100) : he describes fragments in the sandstone 

 beneath the Palisades coming from Green Pond Mountain, which stands 

 northwest of the Triassic area. Further detailed study on the position 

 and source of these conglomerates is much needed in order finally to 

 prove or disprove the theories above mentioned. 



The conditions and order of origin of the various strata, — conglom- 

 erate, sandstone, shale, limestone, and coal, — their even, cross-bedded, 

 and ripple-marked structure, and the causes that brought about a change 

 from one to another in this series, cannot be determined with any defi- 

 niteness until the strata are better co-ordinated than they are at present. 



