UPPER SILURIAN. 



233 



and marly sandstones, with some impure limestones, were formed over a 

 portion of the State ; and in some way the strata were left impreg- 

 nated with salt, and also almost destitute of fossils. 



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

 of the Erie Canal. They are 700 to 1,000 feet thick in Onondaga 

 and Cayuga counties, and only a few feet on the Hudson. 



The following sections (Figs. 453, 454, 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 in 

 one section (Fig. 454) by the Niagara (5 c), Clinton (5 h), and Medina 

 (5 a) beds, and overlaid in the other (Fig. 453) by rocks of the 



Fig. 453. 



Fig. 454. 



Lower and Upper Helderberg (7, 9), Hamilton (10 a, 10 h, 10 c) and 

 Chemung groups (11). 



To the westward, they outcrop between Niagara and Lake Huron, 

 and also about Mackinac. 



Through the Mississippi basin, the limestone of the Niagara period 

 is followed directly by that of the next or Lower Helderberg period ; 

 and the Salina period is not represented, unless by some of the tran- 

 sition beds between these limestone formations. 



In Onondaga County, IN". Y., the beds in the lower half are (1) tender, clayey 

 deposits ( marly tes) and fragile clayey sandstones of red. gray, greenish, yellowish, or 

 mottled colors; and in the upper half (2), calcareous marlytesand impure drab-colored 

 limestone, containing beds of gypsum, overlaid by (3) hydraulic limestone. This 

 limestone afforded Dr. Beck, on analysis — Carbonate of lime 44-0, carbonate of mag- 

 nesia 41 '0, clay 13 5, oxyd of iron 1-25. The rock is sometimes divided by columnar 

 striations, like the Lockport limestone, the origin of which is probably the same as for 

 those in that rock (p. 222). The seams sometimes contain a trace of coal or carbon. 



Near Syracuse, there is a bed of serpentine in this formation, along with whitish and 

 black mica, and a granyte-like rock, in which hornblende replaces the mica, making 

 it a syenyte ; there is little evidence of heat in the beds adjoining these metamorphic 

 rocks. (Vanuxem.) (The position of this locality is not now known). 



In the peninsula of Michigan, the formation includes — beginning below — 10 feet 

 of variegated gypseous marls, 14 feet of ash-colored argillaceous limestone, 3 feet of 

 ralcareous clay, and 10 feet of chocolate-colored limestone. (Winchell.) In western 

 Ohio, the beds are 20 to 30 feet thick. 



In southwest Virginia, a few feet of marly shales with a heavy bed of gypsum yield 

 the strong brine of the wells at Saltville. 



