2io The American Geologist. 
< (ctober, 1903 
4. The Madison formation. 
Mr. Aug. F. Foerste, who has devoted a great deal of time 
to the investigation of the Silurian rocks in Ohio, Indiana, Ken- 
tucky and Tennessee, gave the name Madison* with the follow- 
ing definition (Indiana, Dept. Geol. & Nat. Res., 21st Ann. 
Rep., p. 214) : 
"Beneath the Clinton layer at Madison is the banded, brown and blue 
rock which forms the steep walls at the side of the Michigan and Tel- 
egraph roads, and at many of the waterfalls for miles around. Here 
the layers for a vertical distance of 40 to 55 feet present essentially the 
same color, grain and chemical composition. These layers are grouped 
under the name Madison beds." 
On pp. 220-223 (loc. cit.) the Madison is described as fol- 
lows : 
"In the vicinity of Madison, the top of the Lower Silurian is formed 
by considerable thickness of argillaceous limestones, weathering on long 
exposure from light brown, more or less banded with darker brown, 
to even purplish tinted layers. Although not entirely unfossiliferous, 
the fossils in these argillaceous limestones are confined to a few layers, 
and by far the greater part of the layers are without fossil remains. Be- 
neath the banded limestones occur eight feet of the Favistella bed, which 
near Madison seems to form a well marked horizon. The banded lime- 
stones are inclined to form vertical walls owing to their massive char- 
acter, and owing to the wearing away of the softer shales and clays at 
their base. * * * The banded limestones have a thickness of 30 to 32 
feet in the vicinity of Madison and together with the underlying softer 
shales and the included Favistclla beds of the latter, constitute a well 
marked horizon in Jefferson and Clark counties. 
"The typical Madison bed is commonly overlaid by other rock, the 
Clinton being found several feet higher up. This intervening rock is 
commonly a bluish, fine-grained limestone, with fossils, and of no com- 
mercial value. Sometimes it is an ordinary blue limestone, containing 
fossils chiefly along the partings between the different layers. Murch- 
* As the term Madison had already been applied to other formations (see 
Weeks, North American Geologic Formation Names, Bull. U. 8. Geol. Sur., 
No. 191, 1902, p. 248) Mr. Foerste has proposed to substitute the name 
Saluda for Madison (American Geologist, xxx, No. 6, Dec, 1902, p. 369) . 
As there has been no authoritative pronouncement against the duplication of 
formation names, as in the case of the names of genera and species in the 
biologic realm, the writer prefers to use the name first given. It has been 
an accepted principle in geologic nomenclature that the geographic designation 
of a formation is to be taken from its typical exposure. It is as Mr. 
Foerste remarks when proposing to substitute Saluda, "While the name may 
be taken from another locality, the typical exposures must ever remain those 
at Madison, since nature in distributing her most typical exposures has not 
always followed the laws of geological nomenclature." 
The first use of the name Madison for a geologic formation was by Borden 
in 1874, a vear before Madison was applied to a Potsdam formation in Wis- 
consin (Fifth Ann. Rep. Geol. Sur. Indiana, 1874, p. 139). He used it in a 
vague way for the Cincinnati group in southeastern Indiana. Mr. Foerste's 
use of Madison is then tantamount to a revival of an old term but with a 
more precise, restricted application, and in the writer's judgment the name 
Madison should be retained. 
