Ito NEW YORK STATE MUSEUM 
Joh. Walther [1go0o], Joseph Barrell [Geol. Jour., 1908] have, in recent 
years, pointed out the absence of carbonaceous matter in littoral and delta 
deposits as characteristic of an arid climate. 
While thus the salt and gypsum-bearing deposits serve to demonstrate 
the increase of land-locking and salinity of the lagoon and the subarid to 
arid climatic conditions, the black and green Pittsford shales indicate that . 
then the aridity had not reached its climax and that the lagoon or estuary 
still received at certain seasons both clastic sediments and fresh water. 
It is therefore hardly necessary to infer that the eurypterids of | 
the Salina period lived ina brine. It is quite possible that, when the 
lagoon became too saline, they withdrew into the brackish water zone 
of estuaries or deltas. This inference agrees well with the meagerness of 
the marine brachiopod and mollusk fauna with which they are associated, 
the brackish water being still today the least inhabited zone of the hydro- 
sphere on account of its frequent changes in salinity; and it is also in full 
accord with the occurrence of the eurypterids in the Devonic rocks. There 
is no longer any doubt that the Stylonurus of the Catskill beds inhabited 
an estuary with brackish water conditions; and in regard to the Old Red 
sandstones which are currently considered by the British geologists as 
fresh-water deposits, Kayser in his excellent textbook has noted [p. 168] 
that the presence of whole layers of brachiopods and other genuine marine 
shells in the Old Red sandstone of St Petersburg | proves the preva- 
lence, at least temporarily, of brackish water lagoon conditions, and Clarke! 
has described the lagoons indicated by the Upper Devonic deposits of 
eastern New York, comparing these with the conditions prevailing now in 
the bar-locked lagoons of the Prussian Baltic with their shifting of fresh- 
water and brackish faunas. The eurypterid beds of Lanarkshire and the 
Pentland hills, of Ludlow age, are regarded by British geologists as brackish 
water deposits, for the reason that they contain eurypterids, phyllocarids 
limulids, scorpions and myriapods together with fish and land plants. It 
therefore seems proper to conclude that the eurypterids in Siluric time 
1 Naples Fauna in Western New York. N. Y. State Mus. Mem. 6, 1904, p. 206, 
