INDEX. 167 



Page. 



Prairie du Chien, geology of - - ^ .'' 125 



Primary rocks, application of the term - - 25 



R. 



Red sandstone group, deficient in the United States ' . 51 



Rocks, chemical nature of - 26 



Mechanical nature of - 26 



Appearance of, changed by ignigenous bodies - - 27 



Earliest fossiliferous - - 32 



Cause of their inclination - - 40 



Deceptive stratification of - 41 



Unconformable - - 42 



S. 



Salt, below the coal measures in the United States - 92 



Saliferous strata in the United States - 115 



Near Abingdon, Virginia - 116 

 Secondary beds, those not reached by tide-water lie west of the Alle- 



ghany ridges - 43 



Fossil plants of . - 88 



Sedimentary rocks, origin of - 18 



Serpentine - ... 30 



Overlying sedimentary limestone - - - - 31 



Silurian system, new arrangement of, by Mr. Murchison - 26 



Explanation of - . - - - - 33 



Origin of the term - ... 34 



Equivalent of the grauwacke beds - - 35 



Valley of the Potomac . 42 



Do. do. - . 101 



At Flintstone, Maryland . - 103 



Sioux, origin of the term - - - - . . 128 



Slate, mica . . 28 



Talcose - v> -,. - ' * --: - 29 



Micaceous, Potomac \ . . 96 



Springy land, cause of - . ' r . .8 



St. Peter's river - .... 135 



Indian name and course . .- . ' 137 



Passes through Bois Franc - . 139 



Limestone in place - . 140 



Change of mineral formation - - 146 



Granite in place - ... 147 



Grand Portage and laminated rock - - 149 



Its sources - . " ' .* - . . . 153 



