THEIR DEPOSITS AND DRAINAGE. 651 
to the moisture of the surrounding country. The reason 
why the walls of this cañon stand up in such awful preci- 
pices of thousands of feet is, that the perennial flow of the 
stream is derived from far distant mountains ; almost no rain 
falls upon its banks, and when any portion of the bordering 
cliff has passed beyond the reach of the stream, it stands 
almost unaffected by atmospherie influences. 
On the east of the Roeky Mountains lies the country of 
the "plains," a region not unlike in its topography to the 
great plateau of the West, but differing in this: that it is not 
bordered on the east by a continuous mountain chain ; that it 
slopes gently downward to the Mississippi, and that its east- 
ern half has been so well watered that the valleys have been 
made broad and all its topographical features softened down. 
In former times, however, the topographical unity now con- 
spicuous on the plains did not exist, and the surface was 
marked by a series of great basins which received the flow 
ef water from the Rocky Mountains and formed lakes, less 
numerous, it is true, but of greater extent than those of the 
far West. The northern portion of the eastern plateau has 
been Dr. Hayden's chosen field of exploration for many 
years; a field he has well tilled, and from which he has ob- 
tained a harvest of scientific truth which will form for him 
an enduring and enviable monument. l 
Among the most interesting researches of Dr. Hayden in 
this region, are the studies he has made of the deposits 
which have accumulated in these great fresh-water basins. 
The story he has written of his explorations of this district ` 
has been so well and fully told that I shall not attempt to 
repeat it. Suffice it to say, that the series of fresh-water 
basins discovered by Dr. Hayden in the country bordering 
the Upper Missouri have proved to be as rich in new and in- 
teresting forms of animal and vegetable life as any that have 
been found upon the earth's surface. The vertebrate remains 
collected by Dr. Hayden have been studied, described and 
illustrated by Dr. Liedy, and the splendid monograph which 
