294 GEOLOGICAL SURVEY OF THE TERRITORIES. 



of tall, waving? jjrass, interrupted every twelve or fifteen miles by a 

 narrow fringe ot trees, chietly oalv, that lines the bank of some tributary 

 which Hows into it from the east or west. The descent of the stream 

 northward, counting along- a direct line, is about one foot to the mile, 

 but if we follow its windings the fall will be less than this amount. 



Passing westward beyond this valley we observe a very di.^tinct 

 change in the scenery. Here the treeless plains spread out before us in 

 long, rolling swells, in that peculiar and somewhat semi-gloomy grandeur 

 which belongs alone to the great trans-Mississippi plains, of which this 

 is a i)art. The surface gradually ascends and becomes more undulating, 

 broken into long, low, rounded ridges, smooth, grassy knolls and hil- 

 locks, furrowed here and there by the narrow, deep canon-like valley 

 of some stream, or by a dry coulee, which marks the pathway of some 

 ancient creek or river. Instead of the forests of the eastern basin, or 

 the tall, waving grass of lied Kiver Valley, we now see the low, pale- 

 green sward, or, as we move farther into the interior, the short bunch- 

 grass, which formed the favorite food of the immense herds of buffaloes 

 and antelopes that once roamed over these }>lains. Here and there we 

 see a lake amid the somewhat barren surroundings, but the while in- 

 crustations on the bowlders which line its shores tell us too truly, what 

 our taste confirms, that its waters are brackish, mostly unfit for the use 

 of man or beast; a few fresh- water lakes are found, but these are rare. 

 Another feature, which causes us to have doubtful forebodings of the 

 distant future, is the frequency of what are significantly termed " dry 

 lakes." These are the dry and ])arched basins wliere but a compara- 

 tivel}' few years past lakes existed, not in the distant geological past, 

 but in several instances within the memory of those now living. The 

 surface of the country between the valley of Red Kiver, on the east, 

 and Missouri Eiver, on the west, may be described, in general terms, as 

 consisting of high, rolling prairies, inteisected by the valleys of a few 

 streams which run south. But this general contour is interrupted by 

 two elevated plateaus, which stand high above the general level as 

 monuments reared by the vast aquatic forces of the past, as if to give us 

 some idea of their stupendous i)ower. The smaller of these elevated 

 plains, the Coteau des Prairies, extends from a point about forty miles 

 west of the north end of Lake Traverse, latitude 40° and longitude 

 97° 30', southward, expandiug and somewhat dividing toward its south- 

 ern extremity. The western arm of this southern extension encroaches 

 close upon James Kiver Valley, about latitude 44° 15', where it eiuls ; 

 the other arm reaches southeast, passing down on the east side of the 

 head-waters of Big Sioux, and gradually fades out in the southwest 

 corner of Minnesota. The elevation of its surface averages nearly 2,000 

 feet above the level of the sea, varying from 1,800 feet to 2,040 feet, 

 showing a rise above the plains east of it of about 800 feet and above 

 the valley west of it of 700 feet. 



The other plateau is the Coteau of the Missouri. This hugs the val- 

 ley and follows the course of the Missouri northward from Fort Sully to 

 the great bend of the river near the n)outh of the Yellowstone. Here it 

 recedes and extends in a northwest direction into British Possessions, 

 where it gradually fades out ami is lost. It varies in width from thirty to 

 fifty miles and in height Irom 1,800 to 2,200 feet above the sea; but the 

 surface is more irregular than that of the other coteau, jMjrtions of it 

 rising as much as 200 feet above the general average. The general ele- 

 vation corresponds very closely with that of the Coteau des Prairies, 

 showing very clearly some relation between the origin of the two. On 

 each are numerous small lakes, mostly iuipreguated more or less with 



