The thickness near the head of Lake Pepin is 185 feet, but south a few 
hundred miles in the State of Missouri it expands to a thickness of 
1,300 feet. It exposes a thickness in northwestern Texas of about 
400 feet, and occurs at many other places in the far west. 
The genera which are first known to make their appearance in this 
eroup, are distributed as follows: 
Among the Protista, Calathiwm occurs in the Quebec and Chazy; 
feceptaculites in the Trenton, Hudson River and Niagara; hab- 
daria, Ribeira, and Trichospongia, are peculiar to it. 
Among the Polypi, Monticulipora occurs in the Chazy, Trenton, 
Utica Slate, Hudson River, Clinton, and as high as the Devonian. 
Among the Gasteropoda, Huomphalus, Murchisonia, and Metop- 
toma, occur in almost every succeeding group to the Coal Measures; 
Subulites in every group to the Guelph; Trochonema and Helicotoma 
occur as high as the Upper Helderberg; Hunema occurs in the Black 
River and Niagara; Maclurea occurs in the Quebec, Chazy, Black River 
and Trenton; and Scevogyra is peculiar to it. 
Among the Cephalopoda, P2loceras occurs in the Quebec. 
Among the Lamellibranchiata, a class unknown in older rocks, 
Cypricardites occurs in nearly every succeeding group to the Carbon- 
iferous ; and Huchasma occurs in the Quebec. 
Among the Crustacea, Dolichometopus occurs in the Quebec. 
Of the nineteen genera mentioned, four are peculiar to the Calcifer- 
ous, five pass into higher groups, but not beyond the Lower Silurian, 
three terminate in the Upper Silurian, three in the Devonian, and four 
in the Carboniferous. 
This group is connected with the Quebec by numerous species, which 
occur in both, among which are Ophileta uniangulata, Holopea dili- 
cula, Helicotoma perstriata, Pleurotomaria caicifera, P. postumia. 
Maclurea matutina, M. sordida, Ecculiomphalus canadensis, Camar- 
ella calcifera, Lingula mantelli, L. irene, Amphion salteri, Bathyurus 
cordat, B. conicus, and Asaphus canalis, the latter also occurring in 
the Chazy. It, also, so graduates into the Quebec, at some localities, 
that no distinguishing line of separation has been observed. 
The Quebec Group.—This group was first characterized, and its. 
position between the Calciferous and Chazy determined, by Prof. E. 
Billings, in 1862. It was further defined in 18638, in the Geology of 
Canada, and its fossils afterward more fully described by Prof. Hall, 
in Decade II. of the Survey of Canada, and by Prof. Billings in his 
Palzeozoic Fossils. 
