158 Stour City Academy of Science and Letters. 
river level in Dakota County, and it carried down many 
of its tributary streams with it. Thus the doubtful sands 
may represent stream or terrace deposits of that stage, 
which failed to be removed and were subsequently coy- 
ered by glacial deposits. 
The true Pleistocene record is found in the deposits 
left by the Ikansan ice sheet. These deposits are thin 
and scattered, as the area lies outside that affected by 
the Altamont moraine. The loess is intimately associat- 
ed with the drift deposits and thickly covers the region 
except in the trough of the Missouri Valley, everywhere 
conforming to the surface topography in such a way as 
to suggest that the ice sheet which extended over the 
region was either too thin or occupied the surface too 
short a time to obliterate the pre-Glacial topography. 
The Altamont moraine presents a gap of about 9 miles 
in Clay County, South Dakota, about 30 miles northwest 
of this area. Through this gap an ice lobe extended down 
the valley of Vermilion River to within 20 miles of the 
mouth of Big Sioux River. Another lobe extended down 
the Big Sioux south of Canton. The drift south of the 
moraine is thin and patchy, being usually not over 15 
feet thick and underlain by beds of fine sand and clay 
showing no signs of disturbance. This indicates that the 
region has not been covered by heavy land ice. 
In the few exposures along the Missouri River 
escarpment in Dakota County showing glacial material 
there was the normal order, beginning at the top, of 
loess, clay, gravel, and sand. An interesting occurrence 
of interloessal till may be seen on the Iowa side near the 
mouth of the Big Sioux. It is described by Todd and 
Bain,? who give the following section: 
INTERLOESSAL TILL NEAR BRUGHIER BRIDGE, SIOUX CITY, 
IOWA. Thickness 
Feet. 
5. Loess, usual character, thickening back on hills to 100 feet or 
TIMOR ene er Oe gas alps ens Oa A teen OLN ean a A 2) SE yO I 20 
(Contains according to Todd, fresh-water shells, Lymnea and 
Cyclas, and Helix hirsuta.) 
4. Till, brownish, with northern pebbles and bowlders. Blends 
A WANE OLN KOLSESTS Pee OR MIM Bees era leas IO Re att Ha it Say eal seal aT yi IEMA Vas 12 
-38. Loess, compact, whitish, silt-like, containing Succinea and other 
J ibsaih aiksateah Toy gia ashes Pham Ne ea eek Ls aT a RO eR a A ares aura Uli St A ile 6 
2. Gravel, coarse, with northern bowlders...................00005 10 
Su TES OTMIORS Si lie ine Ltt erat ianse mea Nei Ne Ue cere iNet Wa daha) rae NRG Ia Naat 12 
aTodd, J. E., and Bain, H. F., Interloessal till near Sioux City, lowa: 
Iowa: Proce. Iowa Acad. Sci., Vol. 2, 1895, pp. 20-23. 
