OF THE NORTHWEST. 5 
“I 
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. 
ALTERNATIONS OF SANDSTONE AND MAGNESIAN LIMESTONE, 
SECTION V. 
ITS RANGE, EXTENT, AND BEARING. 
Tue 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 
* See Section No. 3. S. 
8 
