SALINA PERIOD. 



247 



in one section (fig. 414) by the Niagara (5 d), Clinton (5 c), and 

 Medina {5 b) beds, and overlaid in the other (fig. 413) by rocks 



Fig. 413. 



Fig. 414. 



of the Lower and Upper Helderberg (7, 9), Hamilton (10 a, 10 b, 

 10 c), and Chemung groups (11). 



To the westward they outcrop between Niagara and Lake Huron, 

 and also about Mackinac; beyond, thin beds in Wisconsin and 

 Iowa have been referred to this period. 



In western Canada the formation is underlaid by a limestone at 

 Gait, Guelph, and other places. The Leclaire limestone, of Iowa, 

 has been referred to this epoch, but is now regarded as closing the 

 Niagara period. 



In Onondaga co., N.Y., the beds in the lower half are (1) tender, clayey deposits 

 (called marls) and fragile clayey sandstones of red, gray, greenish, yellowish, 

 or mottled colors ,• and in the upper half (2), calcareous marls and an impure 

 drab-colored limestone containing beds of gypsum, overlaid by (3) an hydraulic 

 limestone. This limestone afforded Dr. Beck on analysis — Carbonate of lime, 

 44.0, carbonate of magnesia, 41.0, clay, 13.5, oxyd of iron, 1.25. The upper 

 division is said to contain acicular cavities once filled by Epsom salt (sulphate 

 of magnesia). The rock is sometimes divided by columnar striations like the 

 Lockport limestone, and the structure has been attributed to the crystallization 

 of the magnesian sulphate (Vanuxem), or else to that of salt or gypsum (Hall). 

 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 granite-like rock. (Vanuxem.) In part of it horn- 

 blende replaces the mica, making a syenite. There is little evidence of heat in 

 the beds adjoining these metamorphic rocks. 



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 calcareous clay, and 10 feet of chocolate-colored limestone. (Winchell.) 



The rocks of this period have not been distinguished from those of the 

 Niagara period in the Appalachian region in Pennsylvania or to the southwest 

 in Virginia. 



The beds, especially those of the upper half, are much inter- 



