1885.] KEW YORK ACADEMY OF SCIENCES. 19 



per Trias. This may be filled by future discoveries, but at pres- 

 ent it must be represented by a blank on our charts. 



No distinctly marked Jurassic fossils have yet been found in 

 North America east of the Mississippi, and the well-marked Jura 

 of the Black Hills, Colorado, Utah, etc., overlies the upper 

 Trias beds to which reference has been made, so that the term 

 Jura-trias which has been used by several of our geologists would 

 seem to be unwarranted. 



Dr. Britton illustrated by blackboard drawings how a line 

 of limestone outcrops which are found upon the northward shore 

 of the New Jersey Triassic area, in his opinion, would seem to 

 indicate that a portion at least of the floor of the Triassic 

 trough is Palaeozoic limestone. 



President Newberry drew attention to the probable Archaean 

 age of the crystalline rocks which form the eastward border of 

 the New Jersey and Pennsylvania Triassic areas ; they being, 

 according to most local geologists, of the same character as the 

 gneiss and schist of New York Island and Westchester County. 



Prof. D, S. Martin remarked that this whole range of crys- 

 talline rocks, which he had been disposed to call the Tide-water 

 Gneiss, from the fact that it forms the limit of tide water in all 

 the rivers of the Middle States, from this point southward, has 

 certain marked peculiarities of mineralogical character, which 

 distinguish it strongly from the gneisses of the Northern Lau- 

 rentian and of the Highlands. In particular, the abundance of 

 sub-silicates and of hydrous silicates is to be noted. In regard 

 to these last, he had often been impressed with the idea of their 

 possible connection with the geological history of the range. 

 The view that he had long inclined to, was similar to that held 

 by Eussell for New Jersey, and by Kerr for North Carolina, viz. : 

 that this gneiss-ridge (whatever its original age) had been long 

 submerged, and was elevated at the close of the Triassic period, 

 thus forming a "divide" between the Triassic belts on both sides 

 of it, which are left as border remnants of a far wider area of 

 deposit. In this vieAV, it is an interesting question how far the 

 long submergence of a region of crystalline rocks like this, con- 

 sidering the pressure with which water would be forced to pene- 



