86 Wisconsin Academy of Sciences, Arts, and Letters. 
Norwalk sandstone member .—The thickest and therefore per¬ 
haps the most important of these members is the one at the top for 
which the term Norwalk sandstone member is proposed. As a rule 
it consists of fine-grained grayish sandstone, sometimes nearly 
white and often with a yellowish or brownish tinge, commonly 
rather massive in its upper two-thirds and more or less thin bedded 
and in even plates 1 to 6 inches thick in its lower third. In thick¬ 
ness this member varies from 0 to over 40 feet. At Norwalk, 
where as usual it is in contact above with the Jordan sandstone, 
it is about 35 feet. In Beans quarry, near Tunnel City, it is 43 
feet thick, at Osceola, Alma, and in the lower Beef Valley about 50 
feet. From these maximum developments the member diminishes 
southeastwardly to 25 feet at Ironton and less than 7 feet in the 
vicinity of Mazomanie. It has not been observed to the east of 
Cross Plains, in which region the Trempealeau formation is ter¬ 
minated above by the Lodi shale member. 
A large and varied fauna has been collected from the Norwalk 
sandstone member; and most of the species are strictly confined 
to its zone. Locally the sandstone is quite bare of fossil remains, 
but recognizable specimens of some of its characteristic species 
have been found in many places. At most of these localities the 
fossils occur mainly or solely in the thin-bedded lower part, but 
the reverse is the case at Norwalk where many were found in the 
upper third and very few in the beds beneath. Osceolia osceola, 
Saukia pyrene, S. leucosia, Illaenurus qnadratus, Eurekia eos, and 
Sinnopea sweeti are the species most commonly found. 
Lodi shale member .—This term is proposed for the usually yel¬ 
low calcareous shale-like sandstone that lies between the Norwalk 
sandstone and the St. Lawrence limestone. This shale member is 
widely distributed, the outcrops being everywhere recognizable 
from Stillwater, Minn., and Osceola, Wis., on the north to Spring 
Green on the south and the vicinity of Madison on the east. 
Locally the characteristically yellow shale is interbedded with 
purple shale, as in the vicinity of Mazomanie, or with layers of 
sandstone and in other places with dolomitic limestone, but even 
without considering the fossils there is seldom any difficulty in 
recognizing the Lodi shale. The thickness of the member rarely 
falls under 15 feet, with approximately 25 feet as the average and 
50 feet as the maximum. 
In view of the frequent miscorrelation of the underlying St. 
Lawrence limestone with the Mendota dolomite it is important to 
