Marsh — Jurassic Formation on the Atlantic Coast. 113 



This typical section represents the successive Mesozoic and 

 more recent formations, from New Brunswick, New Jersey, 

 on a line southeast, through Lower Squankum to the Atlantic. 

 The distance indicated is about forty miles. 



Geological Section in New Jersey. 

 a. Triassic; b, Jurassic; c, Cretaceous; d, Tertiary; T, tide level. 



My explanation was as follows: 



" The change from the fresh-water plastic clays of New Jersey 

 to the marine beds containing greensand over them proves not 

 only the breaking down of the eastern barrier which protected 

 the former strata from the Atlantic, but a great subsidence also, 

 since glauconite, as a rule, is only deposited in the deep, still 

 waters of the ocean."* 



Since my paper was published, I have been over part of this 

 section several times, and found clear indications of the break 

 itself. Moreover, Professor W. B. Clark, of Baltimore, 

 informs me that he finds distinct unconformity between the 

 marine Cretaceous and the underlying Potomac, along the 

 junction of these two formations, at various other points 

 further south. This fact furnishes a strong argument that the 

 marine Cretaceous belongs to a separate formation from the 

 older fresh-water clays, here regarded as Jurassic. 



Another geologist who has written much about the West, 

 but seems to have failed in comprehending the evidence 

 afforded by the vertebrate fossils from well-marked Jurassic 

 horizons, is C. A. White, and as his opinion is frequently 

 quoted, it may be well to correct one of his statements which 

 bears on the question here discussed. In speaking of the 

 Atlantosaurus beds, in 1889, he made this statement : 



" If it were not for their dinosaurian faunas their Jurassic age 

 might well be questioned. "f 



When this statement was made, more than one hundred 

 species of vertebrate fossils besides the Dinosaurs were known 

 from these same Atlantosaurus beds, and among these, the 

 Crocodilians, the Testudinates, and the various smaller reptiles 

 would have been sufficient to demonstrate the Jurassic age of 

 the strata containing them. More important still, several 

 hundred specimens of Jurassic mammals had been found, over 

 a score of species were already described and figured, and these 

 alone were sufficient to prove the horizon Jurassic. 



* This Journal, vol. ii, p. 441, 1896. 



f Proceeding's of the American Association, Toronto meeting, p. 213, 1890. 



