94 The American Geologist. August, 1904. 
feet. In the southern part of Ripley and Dearborn counties 
no sections are known in which the range of this fossil equals 
40 feet. At Versailles, its range is 20 feet. Two miles east of 
Cross Plains, it is 15.5 feet; a single good specimen of Calo- 
poecia cribiformis was found in the upper third of the D siib- 
qiiadrata zone. Two miles northwest of Canaan the range of 
Dinorthis suhquadrata is 26 feet. At Madison its range is 
about 10 feet. 
From these data it may be seen that the vertical range of 
Dinorthis suhquadrata diminishes rapidly southward, also that 
the distance of the lowest specimens of Dinorthis suhqua- 
drata from the Hehertella insculpta layers decreases south- 
ward in such a manner that at the southern exposures the low- 
est specimens of Dinorthis suhquadrata evidently are but a 
slight distance above the Hehertella insculpta horizon. 
e. The Vertical Range of Dinorthis suhquadrata south of 
Madison. 
At Madison the base of the Dinorthis suhquadrata horizon 
is 82 feet below the Clinton, the vertical range of the fossil 
being about 10 feet. At the Pinckney Swan locality, on Sal- 
uda creek, it occurs 75 feet below the Clinton and 65 feet 
above the base of the Waynesville bed. At the mouth of Bull 
creek, it occurs 63 feet below the Clinton, and ranges from 
this point upward for several feet.. This diminution of the 
interval between the base of the D. suhquadrata bed and the 
base of the Clinton is due apparently chiefly to a decrease of 
the interval between the base of the Dinorthis suhquadrata 
horizon and the base of the beds referred to the IMadison. It 
accords very well with the decrease southward of the interval 
between the base of the Hehertella insculpta layer and the base 
of the Madison, shown by the exposures between Franklin 
county and Madison. 
Should the base of the Hehertella insculpta layer turn out 
to be a reliable marker of the base of the Middle Richmcaid, 
the preceding observations would indicate a very rapid dimin- 
ution in thickness of the Middle Richmond from Franklin coun- 
ty as far as the mouth of Bull creek. The Waynesville bed on the 
contrary would not show any important variation in thickness 
between Franklin county and Madison, although south of 
Madison a rapid decrease in thickness would be indicated. 
