282 GEOLOGICAL SURVEY OF THE TERRITORIES. 



includes some of the sources of the great river-systems of the Northwest and of the 

 continent. From this area, since pre-Silurian times, streams have run in all directions 

 toward the ocean. Within this area, in the State of Minnesota, are the headwaters of 

 the Saint Lawrence system of drainage, which enters the Atlantic Ocean toward the 

 east; those of the Mississippi, which enter the Gulf of Mexico toward the south, and 

 those of the Red River of the North, which, taking an opposite course, find the ocean- 

 level toward the north through Hudson's Bay, in British America. This water-shed 

 consists not in the form of a definite and abrupt ridge. 



This fact, which does not find an exact parallel at any other point in 

 the comparatively level portion of the interior of the continent, marks 

 this area as one of peculiar interest in the study of the physical ge- 

 ography of the Mississippi Valley. 



The Mississippi and Ked Rivers form the chief lines of drainage, and 

 it is worthy of notice that these run in exactly opposite directions. The 

 Missouri River, from its great beud in the northwest corner of Dakota, 

 runs a little east of south, the Mississippi almost directly south, while 

 the intermediate waters find their way directly north through Red River 

 to Lake Winnepeg. 



It has been remarked by some writer that geologists and geographers 

 often fail to appreciate the value of the facts they obtain in regard to 

 the direction of the leading streams and elevated ranges of the coun- 

 tries they explore. Although 1 do not claim to be a geologist, yet I am 

 strongly inclined to believe that the fixing of the channels of these 

 streams belongs to the closing scene of the Drift period. And this 

 opinion corresponds with the idea already expressed by Professor 

 Hayden : * 



At a modern period it ia prohahle that the waters of the ocean swept high upland, 

 reaching nearly to the foot of the mountains. The great water-courses had already' 

 been ^narked out ; consequently we find the yellow-marl or loess 50 to 150 feet thick in 

 the immediate valley of the Missouri, but thinning out as we recede from it or the 

 valleys of any of its branches. 



The cuts given in Professor Winchell's report on the survey of Belle 

 Plaine, Minnesota, indicate that he holds substantially the same opinion. 

 But in his geological report, before referred to, and which was received 

 after this report was draughted, he expresses his opinion on this point 

 as follows : t 



The course of the surface drainage is, in this case, (where the drift is very thick,) 

 dependent very little on the character of the underlying rock. But where the drift is 

 lighter, the direction of the subordinate streams is often determined by the bearing of 

 the sedimentary rocks. A stream is most likely to be located in the depression caused 

 by the erosion or other destruction of the outcropping edge of a soft or friable rock, 

 the more persistent formation adjoining it, above and below, forming the divides 

 between it and other streams. Other causes, however, principally those superinduced 

 by undulations in the strata over long distances, so as to cause them to leave the direc- 

 tion of the principal or tributary valleys, and the variations of level brought about by 

 the unequal deposition of the drift during the prevalance of the ice of the glacial 

 epoch, have very generally marked the effect of unequal erosion of the strata on the 

 direction of surface-drainage. 



The direction of the streams of Dakota and Northern Nebraska un- 

 doubtedly falls within the last category, as their channels seldom reach 

 the bottom of the drift. We may, therefore, safely assume that the 

 direction and lines of water-drainage were already marked out at the 

 close of the Quarternary period, and doubtless previous to the last sub- 

 mergence of this portion of the Northwest. 



An examination of the direction of the tributaries of the leading 



* Report 1870, page 175. 



t Geological and Natural History Survey of Minnesota, page 46. 



