2/2 The American Geologist. May, \m>> 
another sandstone reaching to the base of the Mendota* (St. 
Lawrence). The average relative thickness is estimated to be: 
Lowest sandstone, 300 feet. 
Middle shales (Dresbach), 100 feet. 
Upper sandstone (Franconia), 150 feet. 
A similar succession is indicated in Minnesota by such 
evidence as the boring of deep wells affords. The series of 
shales and upper sandstones are well exposed and present 
sufificient distinctness to allow subdivision. The lowest repre- 
sentative of the Cambrian strata in the Northwest, the lowest 
formation of the Basal Sandstone series, attaining a great 
depth on the floor of the Pre-Cambrian basin, is not exposed 
at any point within the St. Croix Dalles area. Therefore the 
fauna of these strata seen at Taylor's Falls and vicinity does 
not represent the earliest faimal characters of the Cambrian 
as it is developed in Wisconsin and Minnesota. The lowest 
sandstone member doubtless carries a fauna as characteristic 
as other divisions of the formation. What variation there may 
be is not yet known. 
The Franconia sandstone includes the third trilobite bed 
of Owen. Several species described by Hall also clearly be- 
long to this formation. The following species are reported 
from Franconia, Minn.: 
Agrauhis [Arionellus) hipiinctatits Shumard. 
Crepicephahis [Conoccp/inlifes) diadciiiatus Hall. 
Dicellocephahis )iiisa Hall. 
Hypse/oconits franvonietjsis, n. sp. 
Other localities have added: 
Agnosfus Josepha. Hall. 
Chariocephalus whitfieldi Hall. 
Crepicephahis iJiinisce?isis Owen. 
Dicellocephahis niisa Hall. 
Lonchocephalus hamulus Owen. 
L. wisconscnsis Owen. 
Ptychaspis [Dicellocephahis) granulosa Owen. 
P. {Dicellocephahis) ininiscensis Owen. 
Ptychoparia {Conocephalites) anafina Hall. 
P. {Conocephalites) nasutiis Hall. 
P. " patersoni Hall. 
P. " perseiis HrW . 
P. " shuniardi HaU. 
*Geology of Wisconsin, vol. I, p. 121, 1883. 
