Feather stonhaugVs Geological Report. 125 



have carried away a vast extent of mineral surface, and that 

 all the great sand deposites from Lake Winnebago, as well 

 as those in the valley of the Wisconsin, the valley of the 

 Wisconsin itself, the coves and dells and coulees between 

 the sandhills, which now so much diversify the face of the 

 country, are the result of the same denuding force. The very 

 great extent of the arenaceous deposites can only have been 

 caused by an ancient breaking up of these incoherent sand- 

 stone rocks. 



On approaching the mouth of the Wisconsin, west-by-south, 

 the right bank of the Mississippi appears, about 450 feet high, 

 and the river perhaps 900 yards wide, its water somewhat 

 clearer than that of the Wisconsin, and the zizania continuing 

 along its banks. Four or five miles N. N. W. from this point 

 Prairie du Chien is seen, a fine flat, where Fort Crawford is 

 built. East of the garrison and on the edge of the prairie there 

 is a fine continuous escarpment of calcareous rocks, from three 

 to four hundred feet high, alternating with sandstone. This 

 limestone very much resembles that in Missouri before allu- 

 ded to ; the beds are horizontal, of a grayish buff color, some 

 of them compact, others with cavities containing crystals of 

 carbonate of lime. These bluffs are cherty towards the top, and 

 where this commences I observed the beds to be occasionally 

 made up of concentric circles. 1 found one mass, nine feet long 

 and six feet wide, entirely made up of such circles, some of 

 which were two feet diameter. It was sufficiently curious to 

 make a drawing of, of which diagram No. 16 is a representation. 

 I also brought a fragment of it away with me. This is a sort of 

 oolitic structure upon a great scale. 



From Prairie du Chien 1 commenced ascending the Upper 

 Mississippi, which flows the whole distance (about 260 miles) 

 from this place to Fort Snelling, near the mouth of the Minnay 

 Sotor or St. Peter's river, through the same formations that 

 prevail on the Wisconsin, the calcareous rock, however, pre- 

 dominating on this upper line. It would not be consistent with 



