GEOLOGICAL SURVEY OF THE TERRITORIES. 283 



streams mentioned will serve to indicate the direction of the descent of 

 the different parts of their basins. Tbus, the tributaries of the Missouri 

 which flow into it below the bend present a very marked contrast in 

 direction ; those on the west side, as Heart, Ree, Big- Cheyenne, White, 

 and Niobrara Rivers, flow almost directly east; while those on the east 

 side, a« James, Vermillion, and Big Sioux, flow almost directly south ; 

 showing clearly that the channel of the Missouri marks the termination 

 of the effect of the descent from the mountains, and that east of it the 

 descent is from the north. But it must not be inferred from this that 

 the descent toward the east absohitelj" ceases at the JMissouri, for this is 

 not correct, as (in Dakota) it continues — as will be seen by the tables of 

 altitudes — as far east as the valley of Red River ; but the channel of the 

 Missouri is the boundary oX the eastward flow. After giving the tables 

 ef altitudes I will again allude to this subject, and mention some other 

 causes for this change of direction. 



A somewhat singular feature is presented by the tributaries of Red 

 River; as a general rule, those on the west side flow southeast and 

 those on the east side southwest until they strike the immediate valley 

 of the river, where they bend abruptly northward. This would indicate 

 a southern descent for the bordering plains, while it is evident the broad, 

 level valley of the river has a slight northern descent. 



Although, as will hereafter be shown by the tables of elevations, the 

 plain from which the waters of the Upper Mississippi are gathered is, 

 in a manner, segregated from the broad western slope, yet the same 

 direction ef drainage is preserved, the western tributaries flowing 

 southeast, while the few eastern ones within Minnesota flow southward. 

 This direction is preserved, notwithstandiug, as in Southern Minnesota 

 the descent of the bordering surface of the country is directly opposite 

 to the course of the streams. 



If we move southward to the latitude of Iowa and iSTebraska, we shall 

 find the drainage almost wholly eastward or southeast, that toward the 

 south being less marked thau in the northern sectioti. In Nebraska it 

 may be said to be entirely eastward, some of the northern tributaries of 

 the Platte only bearing a little southeast. The drainage of Iowa is in 

 great part to the southeast, a few minor streams running southwest into 

 the Missouri River, indicating* a narrow western slope along its western 

 boundary. ♦ 



It is evident that the vertical topography is of the utmost importance 

 in studying- the physical geography of any section, and more especially 

 is this the case where the outlines are not rugged, but where the long 

 rounded swells and apparently level plateaus are calculated to deceive 

 the eye. 1 have, therefore, collected all the data to be obtained on this 

 point, particularly what refers to the surface of Minnesota and Dakota; 

 and fortunatelv the recent surveys of lines through this section of the 

 Northwest for the purpose of locating' railroads have furnished us with 

 sufficient material to enable us to form a tolerable correct idea of its 

 topography. Therefore, before ]n'oceeding further, I insert the follow- 

 ing listsof elevations and distances, which have been furnished in most 

 cases from the officers of the roads mentioned. One or two have been 

 copied from the report of Professor Winchell, heretofore referred to, and 

 some of the tables furnished me have been corrected by this report. 



