50 Bulletin of Wisconslx Natural History Society. Vol. 1, No. 1. 
locality of the fish Rhynchodiis excavatus. In Sections 9 and 10 
of the same township occurs the most northwesterly known out- 
crop, where it has a very slight exposure and rests upon the lime- 
stones of the Niagara formation. On the lake shore, north of the 
village of Whitefish Bay, and about six miles north of Milwaukee, 
there is a very limited exposure of the upper layers of the group. 
This is the typical locality of the Cephalopod Gyroceras eryx.{2) 
In sinking the shaft and tunneling for the present water supply 
of the city, clays and so-called shales of the formation were en- 
countered for the greater part of the distance, the fossils found 
being identical with those from the upper portion of the formation 
at the other localities. 
Exactly how far along the lake shore, or into the state the 
formation may have originally extended will probably never be 
known, as its area has undoubtedly been greatly reduced by the 
eroding agencies of the drift. This is confirmed by the fossils 
of the group having been found at Racine,' Wis., twenty-five miles 
south of the most southerly known exposure of the formation. 
The formation as shown at its different outcrops, in its litho- 
logical character, consists of a blueish-gray or ash-colored impure 
dolomite, which weathers on exposure to a yellowish or buff color, 
due to the oxidization of the iron which constitutes one of its in- 
gredients. Its known impurities consist of sihca and alumina, 
and it also carries considerable magnesia. In texture it varies con- 
siderably, being quite homogeneous in some layers and quite irreg- 
ular and lumpy in others, while between each of the layers there is 
generally a more or less w^ell-defined layer of a semi-hard clay, 
being barely traceable between some layers but ranging up to about 
five inches in thickness between others. In degree of induration 
it ranges from rather soft to moderately hard, except in four of the 
layers, which are more or less exceedingly hard, due to the min- 
eral matter that they contain. The minerals found are calcite, 
iron pyrite, zinc-blende, nickel and bitumen. The chemical com- 
position is well illustrated by an average analysis of the layers 
number two to eleven, which gives : 
Carbonate of lime 45- 11 
Carbonate of magnesia 30.89 
Silica 16.61 
Alumina 4.09 
Oxide of iron 3.25 
99-95 (3) 
2. The third species, that of the Crinoid, Melocrinus nodosus, was described 
from a specimen collected from the drift. Geol. of Wis. 1861. 
3. Geology of Wisconsin, Vol. 1, Page 202. 
