172 F. B. Meek and A. H. Worthen on the Age 
known, as Prof. Swallow has shown, to hold a position beneath 
the Lithographic limestone. In Llinois, however, numerous 
exposures show that the black slate comes in just above all the 
well defined Hamilton Group beds as may be seen by the fol- 
lowing section taken near Jonesborough, Union county, Illi- 
nois :— 
1. Brown silicious shale probably representing the 
Vermicular sandstone and Shale of Prof. Swallow, 50 to 60 ft, 
2. Brack Suarte with its characteristic Lingula, 40 to 50 ft. 
Hamiltonensis, Trepidoleptus carinatus, Helio- 
phyllum Halli, and other well known Hamilton 
species, along with Atrypa reticularis, &c., 120 ft. 
Now as the Chouteau limestone of Prof. Swallow, is known 
the Hamilton Group, renders it very improbable that even our 
western Black slate formation represents the Marcellus shale. 
Its position would seem to be more nearly that of the Genesee 
slate of New York, as suggested by M. DeVerneuil, which sup- 
position is strengthened by the affinities of the only fossils yet 
und in it, viz,—a small Lingula and a Discina, scarcely, if at 
all, distinguishable from species occurring in the Genesee slate 
of New York, to which in fact they were referred by Prof. Yan- 
dell and Dr. Shumard in 1847, 
forms occurring in any other part of the Hamilton grou athe 
i TS 
. 
teau limestone of Missouri, which comes in some distance above 
