312 Dr. Hayden on the Period of Elevation, §¢. 
where the White River beds probably began their origin, we 
. oa 
Qo 
find only the lower strata of this group, usually reposing 
yellow marl deposits. e can only account for these phe- 
nomena on the supposition that this great Tertiary fresh water 
lake had its commenceme the White River valley, and as 
spread itself over the vast area which it now occupies. We thus 
think that, by means of these Cretaceous and Tertiary deposits 
of the West, we can yet trace step by step the progress of tha 
grand development which has given the present geograpiica 
conformation to the West, and originated the fountains from 
which flow those mighty rivers which may well be called the 
commercial arteries of the American continent. _ 
Another illustration of the gradual and Jong continued rise of 
the country may found in the immense chasms or cafions 
which have been formed by the streams along the mountain 
si 
barometl! 
rofiles, already referred to, we see at a glance that in traversing 
he country from the Mississippi to the foot of the mountains 
the ascent is very gradual, but increases as we approa h j 
upheaved ridges. In an equal proportion will the rapidity rs 
‘ re 
e descent is so gradual that the Missou” 
ver its yielding alluvial bed, transpor¥%8 
the Gulf of Mexico 
% 
* 
