167 



Page. 



Prairie du Chien, geology of - - - - - - 125 



Primary rocks, application of ihe 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 = 29 



Micaceous, Potomac ----- = 96 



Springy land, cause of - - - - - =8 



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



Indian name and course - - . . . 137" 



Passes through Bois Franc ----- I39 



Limestone in place = , I40 



Change of mineral formation - - . - 146 



Granite in place I47 



Grand Portage and laminated rock - - = . 149 



Its sources - = . - . - - 153 



/ 



