84 The American Geologist. February, 1904. 
occasionally by means of its creeping ability onto lower levels. 
As is indicated by the subjoined map, it is confined to the back 
of the Altamont moraine in the most northern part of the 
region, where it is very feebly developed, becoming more pro- 
nounced beyond the northern limit of Lincoln county at Sioux 
Falls, and even there attaining a thickness that does not exceed 
about 6 feet. As already reported by N. H. Winchell of the 
Geological Survey of Minnesota, the highlands extending 
along the eastern bank of the Big Sioux through Sioux and 
Lyon counties, Iowa, are capped by loess, which shows a thick- 
ness of 10 feet approximately. 
In the southern part of the area the loess is far better de- 
veloped than in the north. Although its thickness here has not 
been ascertained, it has been found to mantle all the higher 
points west of Hudson to Beresford and also between the latter 
town and Alcester, the surface being strewn with numerous 
calcareous concretions which are so characteristic of the loess, 
for which reason they have been called by German geologists 
"loess-kindchen," while the loess itself shows a light buff color, 
grading into deeper and lighter shades. 
In the western part of the area under discussion the loess 
has not been met with, neither along the Vermilion river nor 
along its eastern tributaries, the region between the Vermilion 
and the 96° 50' being chiefly occupied by the "bowlder-clay" 
or till. 
The material of the loess consists, contrary to the till, of 
only two ingredients, viz., minute, more or less rounded grains 
of silica and fine grains of clay, being cemented together by the 
still finer detritus of the two. No pebbles or bowlders are pres- 
ent, and while the till shows no traces of stratification, except 
in its sand-and-gravel-"pockets," the loess exhibits more or 
less distinctly a stratified structure. 
d : The Altamont Moraine and its features within the limits 
of the area. 
The two ridges, which we have already discussed to some 
extent with reference to their importance as water-sheds of the 
region and which exhibit a decidedly moranic character, are 
portions of the so called "Altamont"-moraine. which marks 
the more stationary boundary of the first extensive ice sheet 
of the Wisconsin ice epoch invading the Dakotas during late 
