90 Wisconsin Academy of Sciences, Arts, and Letters. 
position in the valley of Blue Eiver. Indeed, this correlation is 
decidedly doubtful in the case of the basal Trempealeau shale in 
sections where, as at Norwalk and below Beans quarry near Tun¬ 
nel City, the St. Lawrence dolomite member is either absent or 
unrecognizable. In such places the basal shale may well be of the 
age of the St. Lawrence dolomite. Until this question can be fur¬ 
ther investigated and determined it is thought advisable to defer 
proposing a special name for the basal shale. 
The Feanconia Formation and its Subdivisions 
The Franconia formation is divisible everywhere in the western 
half of the State into four, five, or six members, but these differ 
regionally so much in character and sequence that it is difficult 
and as yet impossible to correlate exactly those prevailing in the 
northwestern quarter with those found in the southwestern quarter 
or in either of these with those seen in the middle part of the 
State. 
In the area lying to the south of Trempealeau we can usually 
distinguish two main greensand zones, one—50 feet to 70 feet 
thick—at the top of the formation; the other—30 feet to 45 feet 
thick—in the lower half. The upper of these greensand zones is 
characterized faunally by several species of Ptychaspis, among 
which the most notable is P. miniscaensis. The lower greensand 
contains few fossils. 
Between the greensand members is another usually well defined 
zone—10 feet to 40 feet thick—that differs from the adjoining 
beds in consisting mainly of yellowish platy sandstones of which 
occasional layers often are fiUed with highly characteristic re¬ 
mains of tribolites. These include Ellipsocephalus curtus, Chari- 
ocephalus wJiitfieldi, various species of Ptychaspis, and species of 
the new genus Wilburnia, Walcott ms., including the typical form of 
W. diademata (Hall). 
Under the lower greensand is a fourth member that is dis¬ 
tinguished from the others by its shaly and thin-bedded micaceous 
sandstone and sandy limestone. The latter occurs in the lower 
third of this member and usually is marked by an abundance of 
valves of articulate brachiopods. These belong to two or three 
species of Eoorthis, of which E. remnicha probably is the most 
characteristic. Many small trilobites occur with these and in the 
shaly sandstones above. 
