IOWA ACADEMY OP SCIENCES. 
21 
flowed at a level probably twenty feet higher than at present. 
Number 2 is pi*obably a silt capping which originated in a manner 
analogous to that of ordinary bottom land. The Succinas were 
probably introduced accidentally, as similar shells may now be 
found at the base of the bluffs. Number 3 seems to be a slide or 
wash of till from a higher original level farther back. The drift 
clays lie thirty or forty feet higher a few rods away. Number 4 
is probably the body of a terrace similar to that found south of 
Sioux City. It is true its upper surface is more eroded near 
Riverside, and not clearly distinct from the older loess farther 
north, but the hill-tops of loess do not rise as high as farther 
north and east. 
Somewhat similar deposits occur at Kansas City. Near the 
foot of Lydia street, under many feet of loess are irregular 
sheets and strips of limestone fragments, northern pebbles, 
granite, red quartzite and other rocks. These have a slight 
intermixture of clay, interstratitied with layers of loess. The 
top of the exposure of the pebble beds is about sixty feet above 
the Missouri river near by. It is clearly in the base of a high 
terrace covered with loess. The explanation suggested for 
the Riverside section is quite confidently applied here with the 
modification that the wash is not so clearly till, and the under 
layers of loess are not so regularly deposited. 
The best and clearest example of interloessial till is that dis- 
covered and examined by both the authors within the past field 
season, near Sioux City. North and east of Riverside Park 
there are a number of openings from which sand and gravel has 
been taken. These usually expose in regular order, loess, 
brown clay, a thin gravel bed and sand. In one of them, how- 
ever, a bed of till was found interstratified with the loess. This 
exposure is about one mile northeast of the Brugier bridge, 
over the Big Sioux river, and is about 150 feet above that 
stream. It is as high as any drift exposure in the vicinity. 
The till is typical boulder clay, consisting of dark brown clay, 
through which is disseminated pebbles and boulders of northern 
rocks, such as are found lying at lower levels in the drift of the 
vicinity. Among the rocks identified is the Sioux quartzite, 
which is indicated by a hammer at the left of the plate. The bed 
of till is of variable thickness, being a little over six feet at the 
left of the pit and tapering from that toward the right to a 
feather edge. While the whole width of the bed is not exposed 
the outline seen seems to indicate a lense- shaped body, quite 
