282 GEOLOGICAL SURVEY OF THE TERRITORIES. 



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

 continent. l'"'roui this area, since pre-Sihuiaii times, streams Iiave run in all directions 

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

 the Saint Lawrence systfm of drainai^e, which enters tho Atlantic Ocean toward the 

 east; those of the Mississippi, whicli enter the Gulf of Mexico toward tli(>, south, and 

 those of the Red River of the North, which, tnkiuy an o])posite .course, tiud the ocean- 

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

 consists not in the form of a delinite and ahrupt ridge. 



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

 the comparatively level portion ot the interior of th(^ continent, marks 

 this area as one of ])ecnliar interest in the study of the physical ge- 

 ography of the Mississi|)i)i Valley. 



The Mississippi and IJed IMvers form the chief lines of drainage, and 

 it is worthy of notice that these rnii in exactly op[)osite directions. The 

 Missonri River, from its great bend in the northwest corner of Dakota, 

 rnns a little east of sonth, the ^lississippi almost directly sonth, while 

 the intermediate waters hnd tlieir way directly north through Ited liiver 

 to Lake Winnepeg. 



It has been remarked by some writer that geologists and geographers 

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

 tlie direction of the leiidiitg 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 i)eriod. And this 

 opinion corresponds with the idea already expressed by Professor 

 Hayden : * 



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

 reaching- nearly to tho foot of the mountains. The great watcr^courses had already 

 been marlxcd out ; consequently we find the yellow-marl or loess fiO to 150 feet thick in 

 the innnediate valley of the Missouri, hut thinning out as we recede from it or tho 

 valleys of any of its branches. 



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

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

 But in his geological re})ort, before referred to, and which was received 

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

 as follows:! 



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

 dependent very little on the character (jf the nnderlying 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 tho erosion or other destruction of the outcropping edge of a sofr, or friable rock, 

 the more persistent formation adjoining it, above and below, forming tho 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 unecpial deposition of the drift (huing the ]>revalance of the ice of the glacial 

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

 direction of surface-draiuage. 



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

 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 Avere 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 1H70, page 175. 



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



