LOWER SILURIAN. 



183 



resenting the whole Canadian period, from the St. Peter's sandstone 

 to the Calciferous. In the vicinity of Carp River, Whitney observed 

 this sandstone resting unconformable on the Archaean, as represented 



Unconformability at Carp River, Michigan. 



in the preceding sketch (Fig. 283) by him. The Archaean rocks evi- 

 dently stood there as a seashore ledge, when the sands of the sand- 

 stone were deposited. 



1. Calciferous epoch. — a. Interior Continental basin. — In New York and Can- 

 ada, the Calciferous formation often consists below of impure magnesian limestone of a 

 dark gray color. In many places in northern New York, the layers are very hard and 

 siliceous, and contain geodes of quartz crystals, as at Diamond Rock, Lake George, and 

 at Middleville and elsewhere in Herkimer County, etc. The mixture of calcareous with 

 hard siliceous characteristics is a striking peculiarity of the rock. Owing to the lime 

 present, much of it becomes rough from weathering. Besides quartz and calcite, 

 barite, celestite, gypsum and occasionally blende and anthracite, are found in its 

 cavities. The limestone often contains chert or hornstone.- 



The "Lower Magnesian Limestone" of Missouri, mostly unfossiliferous, is referred 

 by Swallow to the Calciferous epoch. He makes it to consist of four limestone strata, 

 190 to 350 feet thick, which he numbers, beginning above, 1 to 4, and, between these, 

 thinner strata of sandstone, 50 to 125 feet thick. Shumard has described fossils from 

 the third which are regarded as Calciferous. In the other strata, above, the rest of the 

 Canadian period may be represented. In Wisconsin, according to Hall, the Lower 

 Magnesian limestone is in all only 200 to 250 feet thick ; and at top there is the St. 

 Peter's sandstone, mostly 60 to 100 feet thick, referred to the Chazy. Farther north, 

 near Lake Pepin, there are, beneath the Magnesian limestones, several hundred feet of 

 sandstone, probably Calciferous in age. Along the south shore of Lake Superior, on 

 Keweenaw Point and elsewhere, there is sandstone only. On Keweenaw Point, it under- 

 lies at one or two places a thin, fossiliferous limestone of the Black River and Trenton 

 age, showing that it is older. The rocks on Keweenaw Point include 8,000 to 10,000 



