Glacial Lake Nicolet. — Upham. 109 
Farther northeastward the Fox valley widens, and a water 
deposit of reddish clay overspreads the lowlands along- its 
course. The same deposit extends also up the Wolf valley, 
tributary to the Fox from the north, and it likewise surrounds 
lake Winnebago. Its area westward from that lake was 
mapped approximately by Gen. G. K. Warren, who regarded 
this clay as the sediment of lake Winnebago when greatly ex- 
tended at some former time, since the Glacial period, and out- 
flowing past Portage to the Wisconsin river.* 
More detailed examination and mapping of the old lacus- 
trine deposit were done by Prof. T. C. Chamberlin, who found 
that it continues northeast to Green bay and lake Michigan, 
and reaches thence a long distance south, adjoining the lake 
shore. He writes of this red clay as follows :t 
It differs most obviously from the bowlder clay, in possessing a deep 
reddish or purple color, which weathers at the surface to an ashy drab, 
while the bowlder clay, although not infrequently reddish or even purple, 
is usually blue or drab, and differs also in the great irregularity of its 
coloration. Hence the formation in question is everywhere known as 
the "red clay." It likewise differs from the bowlder clay in respect to 
the rock fragments contained in it. In the bowlder clay these are ex- 
tremely abundant, and of all sizes, from mere pebbles to those of many 
tons weight. In the red clay, where they are not entirely absent, they 
are, with rare exceptions, small, seldom exceeding six inches in diam- 
eter, and more frequently they are mere hand specimens. The great ma- 
jority of these fragments are of magnesian limestone, and were ap- 
parently derived from the Silurian formations prevalent in the region. 
.... Occasionally a bowlder of considerable dimensions occurs within 
the formation, but there is a very marked difference between this form- 
ation and the bowlder clay in that respect. This fact becomes a very 
conspicuous one in examining adjacent areas, occupied by the two form- 
ations. The surface of the red clay is comparatively free from bowl- 
ders, while they occur in the very greatest abundance on the surface of 
the bowlder clay. It may be here remarked that there is no such 
abundance of bowlders on the surface of the red clay district as to sug- 
gest any other origin than that of wash from the formation itself. The 
clay which constitutes the chief element is highly calcareous in char- 
acter. It contains also a considerable portion of finely comminuted 
quartzose material, in addition to true aluminous clay, so that while 
the whole is quite compact and impervious, it yet has not that extreme 
toughness and adhesiveness that is possessed by the typical aluminous 
clays. 
* Report on the Transportation Route along the Wisconsin and Fox rivers, 
in the State of Wisconsin, between the Mississippi river and lake Michigan, 
1876, p. 88. with maps. 
+ Geologry of W.seonsin, vol. ii. 1877. pp. 221-4, with maps. 
