98 The Ametican Geologist. February, isco 
ly during the deposition of the loess. If the last be true, it adds 
another complication to the problem of the origin of the loess. 
If the James valley was not a pathway for ice during the 
Kansan stage, then, if the till in Kansas is really of the Kansan 
stage, the ice forming it advanced from the Des Moines valley, 
and the first excavation or the re-excavation of the trough of 
the lower Missouri is post-Kansan and post-loessial. This the 
writer urged in his Missouri report,* where he also pointed 
out an adequate cause for the subsequent great erosion, in the 
floods of water coming from the whole western margin of the 
retreating ice-sheet, as well as from the eastern slope of the 
Rocky Mountains; but he refrains from theorizing further till 
we have considered other recent observations. We shall find 
some difficulty with this view. 
//. Old Soil in the iBig Sioux Valley. — Early in September, 
1898 the writer, with Mr. Bain, of the Iowa Geological Sur- 
vey, and ^Ir. Leverett, of the U. S. Geological Survey, visited 
some instructive localities near Sioux Falls, which had at- 
tracted the attention of the writer: first, in his examination of 
the region in 1884, and later, during the season of 1897. Allu- 
sion is made to former obsers^ations in Bulletin No. i, of 
the South Dakota Geological Survey. In the grading of 
streets in Sioiix Falls, at several points, a dark band resem- 
bling soil was noted. This is true more particularly north 
and west of the brewery. This band was first explained by 
the writer, as marking a temporary flood-plain of the Big 
Sioux during some stage of the occupation of the outer mo- 
raine. He was unable to find evidence of its extending very 
far from the stream. The soil was underlain by till, and also 
overlain by that which seemed to be of nearly the same age. 
During the recent visit, not only were these localities re- 
examined, but others, developed by more recent grading, were 
observed near the postofifice, and a more notable example was 
found a mile or more northeast of the postoffice, in cuts 
along the Illinois Central railroad. At the latter point, there 
were found distinct traces of a buried pond, somewhat like a 
basin of the present. In its deeper portions, there is a depth 
of several feet of dark soil, containing numerous fresh-water 
shells — Valvata, Planorbis, Limnea, and also fragments 
♦Missouri Geological Report, vol. X, pp. 213, 215, and 203. 
