ft i 



MUSEUM OF COMPARATIVE ZOOLOGY. 



303 



ment against it. 



monoclinal theory was impossible because the great depth that it re- 

 quired for the sandstone was disproved by the visibihty of the old foun- 

 dation rocks at certain points within the Triassic belts {h; c, 166-171 ; 

 d; g, 671, 7G1). Mather replaced the river by ocean currents, but oth- 

 erwise accepted this explanation. Whclpley thought the largo and small 

 sandstone areas of Connecticut once connected by a general, oblique 

 deposit, since eroded except where trap intrusions preserved it. This 

 theory has gained few advocates. Oblique deposition on so large a scale 

 and at so uniform a dip as sometimes occurs over large areas is impos- 

 sible ; and as has already been pointed out, the occurrence of plentiful 

 conglomerates on the dip side of the sandstone belts is a strong argu- 



The unsymmetrical form of footprints, as if made on 

 a sloping surface (IL D. Rogers, d), is too exceptional to be of much 

 value (Hitchcock, h, 17). On the other hand, it need not be claimed 

 that the layers were absolutely horizontal when formed. Some small 

 share of their present dip may be original. 



Second Theory, — The theory of anticlinal remnants was first proposed 

 for North Carolina by Kerr, in 1874. It was extended by Bradley (289) 

 to Connecticiit and New Jersey, in 18 76, and proposed for the same 

 region independently by Russell, in 1878. Heinrich suggests a some- 

 what similar explanation for the several sandstone patclies in Virginia 

 (249), but later considers each estuary isolated (251). The objections 

 to this theory arc well set forth by Dana {g)] it has the serious defect 

 of resting on negative rather than positive evidence; it fails to explain 

 the general absence of trap in the intermediate region, and the occur- 

 rence of such an isolated sandstone patch as that of Waterbury, Conn.; 

 the amount of erosion it requires is something enormous ; the occurrence 

 of conglomerates along the outcrop side of the sandstone belts has already 

 been mentioned as arguing against it. (See fig. 29.) 



The Third Theory supposes the entire body of horizontal strata tilted 

 to a uniform dip, and the upper parts worn oE This has been advocated 

 by Hitchcock (c, 221, and later), partly by Cook (&, 174), and more re- 

 cently and decidedly by Leconto (441). Besides the great thickness of 

 strata that this supposition requires, and the enormous erosion it involves, 

 not only of sandstones but of the older rocks on one side, the theory is 

 based on the assumption that there is no faulting or reversal of dip ; and 

 this is not proven. If lack of visibility sufficed to prove the absence of 

 faults, it might be said that there are none in Pennsylvania, Virginia, 

 and Tennessee; for fault-planes are hardly ever seen there; they are 

 lines of weakness, and are always covered with detritus. Their exist- 



