Story of the Mississippi- Missouri. — Clayp)ole. 361 
nearly filled the channels of the streams. The greater part of 
the sands so deposited were carried away by the erosion which 
followed the general uplifting of the region ; but this mass is 
in a sheltered position on the down-stream side of projecting 
rocks, and so withstood erosion. It is the counterpart of 
remnants in similarly sheltered places of much thicker masses 
of gravels and sands, some of which are overlaid by loess, in 
the caiion of the Mississippi river ; but the greater part of the 
pebbles and sands of these deposits can be traced to their 
origin in glacial drift, and were evidently carried forward, 
from where the glacier left them, by the river or its tribut- 
aries and dropped upon its bed. Moreover it has been shown, ^ 
that the deposition of loess in the Mississippi Valley was in 
part, at least, contemporaneous with that of glacial drift, and 
the material of the loess itself has been shown ^ to be in part 
at least made up of the finer portions of glacial debris sorted 
and moved forward by water. 
In those portions of Brazil which came within my field of 
observation there is no glacial drift and there are no glaciated 
rock surfaces or glacial topography or other signs of the ex- 
istence of glaciers, and the material of the loess there is wholly 
a product of erosion by water. But in both Brazil and the 
Mississippi Valley loess is a deposit made upon a loiu-hjing 
region hy the overUow of overloaded streams., that is, hy the 
oversow of streams hearing to the region more sediment than 
they could carry through it with the descent and consequent 
velocity of their current due to its elevation. 
THE STORY OF THE MISSISSIPPI-MISSOURI. 
Dr. E. W. Claypole, Akron, O. 
For the purposes of this paper the geological history of the 
North American continent may be divided into four ages, the 
Archaean, the Palaeozoic, the Mesozoic and the Tertiary. The 
telescope of geology has revealed to us more or less of the 
details of all these four great eras but, as might be expected, 
with very different degrees of clearness. Concerning the first 
it is not too much to say that we are only just beginning to 
make out through the vast distance which separates it from 
*ByN. H. Winchell in the sixth annual report on the geology of 
Minnesota. 
2 By T. C. Chamberlin & R. C. Salisbury in the sixth annual report 
of the U. S. Geol. Survey. 
