THE EURYPTERIDA OF NEW YORK 107 
lar to the one at the base of the Salina. Above the Eurypterus beds 
follows the Cobleskill limestone, and here again are representatives of the 
Niagara-Guelph fauna. 
If the cycle just described is considered as produced by the desicca- 
tion of a closed basin, in which extreme salt pan conditions prevailed at 
its climax when the thick beds of rock salt were deposited, it follows as 
a manifest corollary that the eurypterids of Salina age had their biologic 
optimum in a sea of greater salinity than the typical mollusks and 
trilobites of the Upper Siluric could endure. 
In view of the hypotheses before us and the evidence that the euryp- 
terids flourished in brackish and fresh water in the Devonic and Carbonic 
this corollary requires a closer study. 
The English geologists, notably Hugh Miller and Lyell, in the middle 
of the last century, explained the origin of salt deposits by the evapora- 
tion of sea water in basins so separated from the ocean by shallow bars 
that the evaporated water could be replaced by new marine water while 
the corresponding more saline water could not flow out on the bottom. 
This bar theory has been based on safe physical and chemical data by 
Ochsenius,' while von Koenen’? and others have shown that this theory 
on the whole explains the complex composition of the German salt 
deposits. 
A close analysis of the Salina sections and of the character of the 
Salina rocks also suggests this conception as fully competent to explain 
the conditions surrounding their deposition. 
The facts which we consider as of especial importance to a correct 
view of the physical conditions of the Salina sea are: (1) the continuous 
alternations of gypseous and dolomite beds, (2) the great thickness of 
the salt beds. 
‘Zeitschrift fur Praktische Geologie, Mai und Juni 1893; see also Kemp, 
Handbook of Rocks, 1904, p. 106. 
*von Koenen, A., Zur Entstehung der Salzlager Nordwest-Deutschlands. Excerpt 
aus Nachr. der k. Gesellsch. der Wissensch. zu Géttingen, 1905. 
