Editorial Comment, 
111 
Silts nearly im- 
pervious to 
water (two 
kinds, name- 
ly, white 
clays, and 
gumbo). 
Nearly still wa- 
ter; but wind 
may have had 
an influence 
in the deposi- 
tion of the 
white clays. 
White clays cover much of southern 
Illinois south of the Shelbyville mo- 
raine, as far west as the Mississippi 
loess, east to the Wabash loess, and 
south to the Ohio river loess. Gum- 
bo is found along the main rivers, 
on some bottomlands. 
Peaty and 
marly. 
Vegetal accu- 
mulati o np, 
and shell 
deposits. 
Locally over the greater part of the 
state,wherever drainage is imperfect. 
Peat is rare south of the latitude of 
Springfield, but it abounds in the 
northeastern quarter of the state, in 
bogs. M arl deposits are less extensive 
than peat,but are fully as widespread. 
One of the most important results of Prof. Whitney's analy- 
ses is the demonstration that the typical loess contains much 
less fine material (under .005 mm. in diameter of grains) than 
the impervious silts, or than the boulder-clay or till. The 
loess has no coarser particles than these silts, and not socoa-is< 
as the sandy, gravelly, bouldery till, which was amassed by the 
ice-sheet. That the loess is assorted in this way, together 
with the fact that its chief distribution is along the principal 
waterways, seems conclusive proof that it was deposited by 
water and not by wind. Professor Whitney has shown that 
the porosity of soils, dependent chielly on the fineness or 
coarseness of their particles, is usually a far more important 
cause of their fertility or barrenness than the chemical consti- 
tution of the materials of which the soils are composed. 
Glacial Drift of Chicago and its Vicinity. 
A few steps distant from the foregoing, other cases of 
specimens and small pyramids constructed of glaciated boul 
ders and pebbles displayed the very instructive collection which 
has been made by Mr. Ossiau Guthrie, of Chicago, from the 
drift in that city and its vicinity, his interest in this subjed 
having been aroused about eighl years ago during investiga- 
tions of the canal routes for the drainage of the city area to 
the Des Plaines river. Many boulders were here exhibited 
which had been obtained from the till inexcavations forfoun- 
dations of Chicago buildings, son t these having been 
derived from rock outcrops hundreds of miles distant in 
Canada, while others occurring almost in contacl with tin 
Canadian erratics were from the Niagara limestone under! v 
