348 The American Geologist. 'i""^- ^''"'^■ 
B. Decrease ix thickness of the Richmond group. 
I. Indiana. 
Tile Rieliinond stage. 
At Fort Recovery,''' in the southwestern part of IMercer 
county, Ohio, a bed of fossihferous limestone was struck in a 
gas well, at a level of 270 feet beneath the Clinton. The fos- 
sihferous limestone continues for a depth of thirty feet. The 
rock is almost entirely made up of Dajuianella jiigosa. The 
thickness of the Richmond stage at Fort Recovery is therefore 
about 300 feet. From this point southward, as far as Raywick, 
in the western part of Marion county, Kentucky, a distance of 
200 miles, the Richmond stage becomes constantly thinner. 
Between Fort Recovery, Ohio, and the Brookville-Laurel 
section, in Indiana, a distance of seventy miles, the thickness 
of the Richmond diminishes from 300 to 250 feet, an average 
diminution of .7 foot per mile. Between Brookville (250 feet) 
and Versailles (217 feet), a distance of thirty miles, the aver- 
age diminution in thickness is i.i feet per mile. Between Ver- 
sailles (217 feet) and Madison (178 feet), a distance of twen- 
ty-five miles, the average diminution is 1.6 feet per mile. Be- 
tween Madison (178 feet) and Hanover (169 feet), a distance 
of five miles, the average diminution is about 1.8 feet per mile. 
Between Hanover (169 feet) and the Pickney Swan locality 
on Saluda creek (140 feet), a distance of five miles, 
the average diminution is about 5.8 feet per mile. Be- 
tween Saluda creek (140 feet) and Marble Hill (iii feet), 
a distance of 3.5 miles, the average diminution is 8.3 feet per 
mile. Between Marble Hill (iii feet) and the mouth of Bull 
creek (83 feet), a distance of eleven miles, the average dimin- 
ution of the Richmond stage is 2.5 feet per mile. 
The Middle and Lozeev Richmond. 
As far south as Hanover, Indiana, DahnaneUa jngosa is 
very abundant at the base of the Richmond stage, its range 
extending through the greater part of the Lower Richmond. 
At the Pinckney Swan locality on Saluda creek, it is abundant 
only in a f(^w feet of rock- at the base of the Richmond sec- 
tion. At ^Marble Hill, a few specimens were found in the few 
inches of sandv limestone at the very base of the Richmond 
* Geology of Ohio, vol. vi, 1888, p. 263. 
