OF THE NORTHWEST. 



57 



towards Apple River, but it appears to be less sandy in that direction, and is of a 

 better quality, owing to admixture of more calcareous matter. 



It is difficult to explain how, in certain situations, even these easily disintegrating 

 beds of soft sandstone have partially withstood the action of forces that have swept 

 away the surrounding material down to the level of the present prairie. Instances 

 of this occur near Chippewa and Black Rivers, and isolated masses were seen in the 

 vicinity of the Kickapoo, of forty to fifty feet in height ; but the most remarkable 

 examples were observed by Dr. Norwood and Dr. Shumard on the Wisconsin River, 

 below Point Boss, and are described in their reports.* 



I have already remarked that these sandstones, especially towards their upper 

 part, are interstratified with magnesian limestone. Where this is the case, these 

 harder beds, being undermined by the washing away of the intervening sandstones, 

 form overhanging ledges. In such situations, rattlesnakes delight to harbour, and, 

 in the fall of the year, in cool weather, these reptiles may frequently be seen in 

 these warm, sandy nooks and recesses, basking in the sun. This is so common an 

 occurrence in the bluffs on the Mississippi, below Lake Pepin, in the latter part of 

 the month of September, that great precaution is necessary in exploring the preci- 

 pitous slopes of that country. 



The region of country over which Formation 1 is the principal surface rock, lies 

 east of the Mississippi, and north of the Wisconsin River ; bearing from southeast 

 to northwest, parallel with that portion of the Upper Mississippi which is embraced 

 between the mouth of the Wisconsin River and the St. Croix ; forming a zone of 



ALTERNATIONS OF SANDSTONE AND MAGNESIAN LIMESTONE. 



SECTION V. 



ITS RANGE, EXTENT, AND BEARING. 



* See Section No. 3. S. 

 8 



