360 Quaternary Deposits, Etc. — Mills. 
streams in the low l^^ing portions of the region rose to near 
the level of the general surface, and the sediment-charged 
waters spread out in their varying pools of water with little 
or no current, so shallow that vegetation continued to flourish 
and rise through the water. The streams flowed along by or 
through these swampy lands in shallow, shifting channels, 
and along these channels there was current enough to hold 
the finest sediment in suspension, and only sand and gravel 
was deposited there, while the finer sediment was carried by 
the overflowing waters to the right and left and quietly de- 
posited, with only slight variation in coarseness or fineness, 
and obscure, if any, demarcation of laminte or strata, in 
short, with the characteristics of loess. 
At first the loess was deposited but a short distance from 
the water-sheds where the uprise began, but as the uplifting 
went on and its effects extended farther and farther from the 
water-shed, the area of erosive action of the streams was car 
ried forward, and the area over which the streams were depos- 
iting loess moved forward also down stream until the whole 
region had received the sediment, except the highest portions 
near water-sheds. 
The loess of the region is therefore a deposit made when it 
was a low-lying region by the overflow of its streams charged 
with sediment by erosion of portions of their drainage-area 
nearer the water sheds than the place of deposit, which had 
been or were being uplifted. 
The same explanation of the origin of loess meets the re- 
quirements of all its observed conditions in Rio Grande do 
Sul. 
I have compared the loess of Rio Grande do Sul to that of the 
Mississippi valley. The foregoing explanation of the origin 
of loess meets, I think, all the requirements of the conditions 
and characteristics of the deposit in the Mississippi valley^ 
including the occurrence of stems of plants and shells of fresh- 
water and moist-land and dry-land mollusks. But there the 
sediment which obstructed the streams and furnished the ma- 
terial of the loess was in part, at least, derived from glacial 
drift. 
The mass of loose material on the bank of the Rio de Peixe 
of which a section is given above is a remnant of the masses 
of sands and gravels partially overlaid by loess that filled or 
