GENERAL TOPOGRArilY OK Till-: REGION 201 



bending of the sandstone buck to some distance iVoni the fault [)hine in- 

 dicate considerable movement. It is not to be asserted that the contact 

 between the Keweenawan and the Potsdam is everywhere expressed in 

 a fault, but this is a common relationshi}). The contact is everywhere 

 one of unconformity, whether faulting has taken place or not. 



The ranges extend across the state to the Saint Croix river, but in ever 

 diminishing prominence as topographic features. The rocks comi)osing 

 the range dip sharply to the northwest and form the southeastern bound- 

 ary of the great sjnicline in which the western portion of lake Superior 

 lies. South of Ashland the range divides, one portion extending up into 

 Chippewa point, forming the backbone of that peninsula. The other 

 portion, as already indicated, trends across the state and extends into 

 Minnesota. To these ancient ranges is due much of the ruggedness of 

 the region. No very characteristic topography occurs within the ranges. 

 Frequently sharp ridges are found, though a low, broad ridge is more 

 common. The original topography is greatly altered by glacial deposits, 

 and on that account it is difficult to definitely characterize the topog- 

 raphy. The mountain summits form a very even skyline as a whole. 



Between the ranges and the lake there lies a narrow plain, averaging 

 8 miles in width. The underlying rock is the Lake Superior sandstonej 

 already described. It rarel}^ Appears at the surface in outcrops, as it is 

 effectually hidden by glacial debris. The sandstone rises high on the 

 flanks of the ranges, in some cases 200 feet above the level of the lake. 

 From this height it slopes gradually toward the lake, where it appears 

 in cliffs which never exceed a height of 60 feet. The surface deposits 

 consist of an underlying till covered by washed deposits of silt. All of 

 the glacial deposits have an intense red and reddish brown color, due to 

 the large iron content, a characteristic which is prominent in all of the 

 Lake Superior dej^osits. 



Most of the streams of the region rise on the northern slo])es of the 

 ranges, though a few of the master streams, like the Montreal and the 

 Bad, break through the ridges in narrow gorges, locally termed "gaps." 

 Where the streams pass from, the older rocks to the sandstone, falls and 

 rapids usually occur. These streams traverse the sandstone belt in nar- 

 row meandering canyons, which indicate the comj^arative youth fulness 

 of the rivers. The opportunity for the erosion of these gorges has come 

 about through the slow withdrawal of the lake, though earth movements 

 may have been a factor as well. The position of the lake level is the 

 position of local baselevel, and as the lake has been lowered, the local 

 baselevel has been reduced correspondingly. New opportunities for 

 stream erosion have been given with this constant lowering of the lake 

 level from the Duluth stage to the present time. This could take place 



