116 THE GEOLOGY OF MINNESOTA. 



[Drift. 



II. THE DISTRIBUTION AND CHARACTERS OF THE DRIFT. 



Nearly the whole state may be said to be drift-covered ; the only excep- 

 tions being the extreme southeastern and the extreme northeastern portions. 

 At any point on the northwestern boundary, as far east as the lake of the 

 Woods, one may start out southward and travel to the Iowa boundary line 

 without seeing any rock in situ except what he might happen to encounter 

 in crossing the valley of the Minnesota river, and except the rare exposures 

 of red quartzyte in Rock, Pipestone and Cottonwood counties. East of this 

 meridian he would encounter occasional exposures of rock along Rainy 

 river, but southward from the northern boundary he would still have almost 

 an equal scarcity of rock exposure, were he to set out again to the Iowa 

 boundary line. In the flat country south of Rainy river, extending as far as 

 the divide between Red lake and lake Pemidji, there are a few outcrops of 

 crystalline rock in the valleys of the Big Fork river and perhaps of the 

 upper tributaries of Red lake. But that district is in general deeply buried 

 under a sheet of drift similar in composition to that of the Red river valley, 

 but less perfectly drained. The drift then is so thick in the region of lakes 

 Pemidji and Winnibigoshish, and generally throughout the central portion 

 of the state, that it does not afford another rock-exposure until reaching the 

 vicinity of Motley. Rock is seen in scattered patches in Todd, Morrison Mille 

 Lacs, Kanabec, Stearns, Benton and Sherburne counties, as well as at 

 Pokegama falls on the upper Mississippi. But toward the south farther, 

 except in the valleys of the Minnesota and Blue Earth rivers, the drift 

 everywhere conceals the rock with an unbroken mantle from 100 to 200 

 and sometimes 300 feet thick. 



East of the meridian passing through the west end of Rainy lake, the 

 rock is more and more frequently seen projecting above the drift, both along 

 the Iowa boundary and in the central and northern portions of the state, 

 especially in the valleys of streams that flow eastward. There is a tract of 

 the state heavily covered by drift east of Pokegama falls, including the 

 St. Louis valley and its upper tributaries, in which many of the streams 

 that enter lake Superior in the state of Minnesota take their rise; but for 

 the most part in the eastern half of the state the streams expose the rock 

 more and more frequently, indicating an attenuation of the drift sheet 



