316 Hilgard on Drift in the Western and Southern States, 
more ancient strata were readily susceptible of denudation, 
they have entered largely, at times almost exclusively, into the 
composition of the Orange Sand strata, we might suppose that 
the surface of the former (which appears to be at least equally 
as hilly as the present one) had been denuded by atmospheric 
agencies during the glacial period of elevation. 
When, after the subsidence of the first rush, the velocity of 
the water had so far diminished as to render it capable of form- 
"ing stratified deposits, these would naturally possess the mixed 
character resulting from a twofold mode of transportation—by 
water, and by floating ice—the former, no doubt, in many cases, 
succeeding the latter, and, by the grinding action of the smaller 
gravel and sand, transforming the angular blocks first dropped 
into the rounded boulders characterizing the drift of Iowa and 
Missouri, and faintly represented by their scattered congeners 
in the Orange Sand delta. 
t would thus seem that the grandly simple means of a single 
elevation and re-depression in the northern latitudes, to which 
; enomena of the ancient glaciers and sea-beaches point us, 
will equally satisfy the conditions required for the formation of 
the Western and Southern Drift. Down to the. later stages of 
the northern re-depression, the predominant slope would every- 
where be southward, so as to collect in the Mississippi valley the 
glacier waters, not only of the whole extent of northern terri- 
tory now tributary to it, but probably also those of the present 
arctic slope of British America, and a portion of that now trib- 
utary to the St. Lawrence. Hence the comparative absence of 
stratified drift from the Northern Atlantic slope of the United 
States; and its presence, on the contrary, on the sea border of 
the Southern States, as stated by Tuomey, 7. c. 
_ As to the Champlain epoch, it would seem to be represented 
in its later part only, by that which in the Western and Gulf 
States has formed the “second bottoms.” In the Mississippi Val- 
Sic A il a i tala Sci 
