Richmond Group in Ohio and Indiana. — Nickles. 211 
isonia hammelli, Holopea hubbardi, a small species of Orthoceras, Lcp- 
erditia caecigena and other fossils are especially characteristic of this 
horizon." 
These upper layers which Mr. Foerste seems to separate 
from his Madison, the writer includes in the Madison division. 
"North and northwest from the typical Madison bed, the top of the 
Lower Silurian rapidly changes its character. It is replaced by a series 
of blue, often rather dark blue, very fine-grained limestones. This lime- 
stone where quarried often seems to be very solid, but it will not with- 
stand weather. The rock often contains Leperditia caecigena, Isochilina 
subnodosa. Lithologically, this rock is similar to the dark blue, fine- 
grained layer forming part of the Murchisonia hammelli layer in more 
southern areas. The first change of the Madison beds northwards con- 
sists in fact in the alteration of the Madison beds, so as to present the 
same lithological characteristics as the blue beds which southward, near 
Madison, only overlie the Madison beds. The fine-grained limestone 
taking the place of the Madison beds, is interbedded with ordinary lime- 
stones, and with clays containing ordinary limestone fossils. Sections 
of this type begin to be exposed in northern Jefferson county, and are 
typically developed at Versailles, along the whole length of Big Graham 
creek, and for some distance northwards. The correspondence of this 
section is very well seen in the exposure immediately north of Ver- 
sailles, where 29 feet of this limestone, with its intercalated beds of clay 
and shale are underlaid by 11 feet of unfossiliferous brownish and blu- 
ish shales, corresponding to the shales at the base of the Madison beds 
near Madison. Below the shales are 12 feet of limestone and shale, con- 
taining Tetradium minor at many levels, and Fai'istella stellata at the 
very base. This is the characteristic horizon for Favistella in southern 
Indiana. 
"From the Baltimore and Ohio Southwestern Railroad northwards, 
all comparison with the Madison beds is lost. The upper strata consist 
commonly of thin or shaly limestones, interbedded with clays, both us- 
ually abundantly fossiliferous. No demarcation can be made between 
these upper strata and the lower horizons of the lower Silurian, corres- 
ponding to the separation of the Madison from the richly fossiliferous 
shales in Jefferson and Clark counties. This means that the Madison 
beds are replaced northwestward by pure limestones." 
The following is from Foerste's report in the 24th Ann. 
Rep. of Indiana, p. 63. 
"In Ohio the Madison beds are replaced by clays and clayey shales 
which are at times mottled with purple and reddish purple and are 
usually devoid of recognizable fossils. Near the crest of the anticlinal, 
from the Miami river westward to the Indiana state line, the clays are 
less often mottled, are more calcareous, and contain more fossils." 
The foregoing quotations give a very fair idea of what beds 
Foerste meant by the Madison beds. The beds were studied not 
