OF LAKE SUPERIOR. 



191 



It is further conceivable, that, north of the sources of the St. Croix, some subse- 

 quent upthrusting of igneous rocks, forming a main axis of dislocation, and shifting 

 northward the original water-shed, might have raised and tilted the red sandstone 

 strata, and thus changed their general plane of deposition from a slight northern 

 inclination to the southeasterly dip they now present ; so that the white and buff 

 beds of F. 1, though they may seem to rest conformably on these red sandstone 

 beds, might merely abut against them, and not, in fact, overlie them at all. 



V O S S I B L E I" It B 9 E N T CONDITIO N 0 V T II E S E T WO BASINS, A FT EK DIST U K B A N C E. 



But, in the general configuration of the Lake Superior and St. Croix countries, 

 there is nothing to verify such a supposition as this, and little to redeem it from the 

 character of a gratuitous, unsubstantiated theory. There is nothing in the country 

 on the St. Croix, near the mouth of Snake and Kettle Rivers, that suggests, or con- 

 firms, the idea of a former summit range, marking the barrier between two vast 

 basins of deposit. With the exception of isolated trap upheavals, exerting on the 

 dip a mere local and very limited influence, the country in question is as level, and 

 apparently as free from all serious disturbances, as any other portion of the St. 

 Croix Valley. :;: 



Again : the general drift deposits of the interior, unfortunately, conceal from view 

 the rocks which form the nucleus of the present water-shed between the St. Croix 

 and the Brule ; so that we have no direct means of determining the age of its up- 

 lift. But, if we judge its interior, as we fairly may, from the character of those 

 exposed metamorphic and Plutonic rocks, shown on the geological map crossing the 

 head-waters of Bad River, which form the continuation of the same water-shed to 

 the east, we are led to the conclusion, that this ridge was formed by one of the 

 oldest disturbances that have given to this region of country its topographical fea- 

 tures ; anterior, in all probability, to the date of such an uplift as we have imagined 

 to have removed, some thirty miles to the north, the original dividing ridge between 

 the waters of the Lake and the Gulf. 



That dividing ridge, also, is, at this point, of elevation too inconsiderable to have 

 reversed the dip of strata over the supposed distance. The rise, on the portage 



* The ridges on either side the St. Croix, in this vicinity, do not exceed from forty to fifty feet in 

 height. Up Snake and Kettle Rivers, above the Falls, some points of cliffs reach a hundred and fifty 

 feet. At the Dalles of the St. Croix, about thirty-five miles further south, and, of course, under any suppo- 

 sition, within the original Mississippi basin, the disturbances are much more considerable, the trap sum- 

 mits on the river extending two or three miles, and reaching the height of a hundred and seventy feet. 



