246 PALEOZOIC TIME — UPPER SILURIAN. 



tensively submerged in the Coal era. Had the absence of these formations been 

 due to deep submergence, — too deep for animal life, — the slopes of some of the 

 mountains — as the Laramie Range or Black Hills — would have borne evidence in 

 the presence about them of some of the beds representing the Lower Silurian 

 and Devonian periods. The larger part of the eastern slope of the Rocky 

 Mountains is covered by Mesozoic and later strata; and hence no certain 

 inference can be drawn as to the extent of this dry land. 



The Niagara period was a period of continental submergence also 

 in Arctic America and Europe at this time. Even Great Britain 

 had its Coral and Crinoidal seas, and limestone formations in pro- 

 gress, — although »the Silurian there contains comparatively little 

 limestone, owing to the fact that the country lies, like the Appa- 

 lachian region, within the mountain-border of a continent. 



Life. — Eemarks with regard to the life of the period are deferred 

 till the closing pages on the Upper Silurian, with a single excep- 

 tion. There is abundant evidence of extensive low flats and 

 marshes over the continent in the Medina and Clinton epochs : 

 the ore-beds of the latter are decisive proof on this point. The 

 absence, therefore, of the remains of land-plants from these beds 

 may be regarded as nearly sure demonstration that no land-plants 

 then existed. Taking this into connection with the evidence from 

 other regions, and the other formations of the period, there can be 

 no reasonable doubt on this point. 



SALINA PERIOD (6). 



Epochs. — 1. Guelph epoch, or that of the Guelph and Gait 

 limestones (6 a) ; 2. Saliferous epoch, or that of the Onondaga 

 Salt group (66). 



I. Rocks : kinds and distribution. 



The Niagara period had covered the sea-bottom mainly with 

 limestones. With the opening of the Salina period there was a 

 change by which shales or marls and marly sandstones, with some 

 impure limestones, were formed over a portion of New York ; and 

 in some way the strata were left impregnated with salt, and also 

 almost destitute of fossils. 



The beds spread through New York, and mostly south of the 

 Erie Canal. They are 700 to 1000 feet thick in Onondaga and Cayuga 

 cos., and only a few feet on the Hudson. 



The following sections (figs. 413, 414, from Hall), taken on a north- 

 and-south line south of Lake Ontario, show the relations of the 

 Salina beds (6) to those above and below, — they being underlaid 



