314 



THE REGOLITH 



istics of alluvial deposits, a portion of which are but reassorted 

 materials from the glacial drift. 



Appropriate Number of Grains of Sand, Silt, and Clat in One Gramme 

 OF Alluvial Subsoil from Illinois 



Diameter 



Conventional 



(a) 



(&) 



(c) 



MM. 



Names 



Chillioothe 



BOOKFORD 



American Bottoms 



2-1 



Tine gravel , 







1 







1-.6 



Coarse sand . 



83 



48 







.5~.25 



Medium . . . 



6,766 



3,428 



6 



.25-.1 



Mne sand . . 



18,660 



29,300 



194 



.1-.05 



Very fine sand 



63,470 



212,400 



151,400 



.05-.01 



Silt .... 



4,670,000 



6,888,000 



12,230,000 



.01-.005 



Fine silt . . 



86,860,000 



116,100,000 



196,600,000 



.005-.0001 



Clay .... 

 Total. . . . 



2,537,000,000 



3,842,000,000 



14,680,000,000 





2,628,608,968 



8,693,233,177 



14,887,981,599 



(a) Terrace of Glacial age. (b) Flood deposits, (c) Post-glacial ter- 

 race (bottom land of Mississippi). 



The processes active in delta formation are manifested on a 

 smaller scale in the gradual silting up of many an inland lake, 

 particularly such as are of glacial origin. 



It is a striking thought that all our lakes are but transient 

 enlargements of pre-existing streams, and will in time, per- 

 haps even before our own species is extinct, become converted 

 into broad expanses of meadow lands; and that our children's 

 children may yet sow and reap from rich and fertile areas which 

 now echo only to the cry of water-fowls, and the blue expanse 

 of which is broken but by wind-born waves and leaping fish. 



The lithological character of the deposits thus formed vary 

 with certain limits almost indefinitely, since everything de- 

 pends on the character and quantity of the silt brought down 

 by the streams. Rarely, if ever, are they clayey, since the finer 

 particles are carried beyond. In nearly all instances they are 

 found to consist of very fine sand, largely siliceous, permeated, 

 often quite blackened, through the presence of organic matter. 

 Such are the mucks or mucky soils of New England. 



So abundant is this organic matter, that when dried, such 

 deposits are used locally for mulching purposes, though in their 

 fresh condition they are sour and almost worthless except for 

 growing sedges and the ranker kinds of forage grass. During 

 the later stages of the process of filling up, deposition of sedi- 



