The American Geologist. 
August, 1904. 
7. Dinorrhis retiorsa 100 
8. Leptaona rhomhoidaliH lOi 
9. Rhj-nchotrema dentatum, ith. ca))ax 101 
10. Plectamboiiites sericeus 101 
11. Platystrophia lynx 101 
12. Streptelasma, Hetercspougia, Ceatricea 102 
I. Variations ix Thickness of Ordoviciax Strata in 
Indiana. 
/. The Subdivisions of the Ordovician of Ohio and In- 
diana. 
The Ordovician of Indiana is merely the western extension 
of the Ordovician of Ohio. It presents the same divisions 
and subdivisions, contains the same fauna, and was deposited 
under closely similar conditions. 
The following subdivisions were proposed by ^Ir. J. ]Nl. 
Nickles :* 
r Madison, Saluda or Upper Richmond 
Richmond. . . \ Whitewater /_ ^^ Middle Richmond 
■^ Liberty ) 
I Waynesville, or Lower Richmond 
^ Warren 
I Mount Auburn 
) Corryville 
j Bellevue 
I Fairmount 
( Mount Hope 
Cincinnati 1 Lorraine. 
Trenton 
I 
I 
I I Upper Utica 
LUtica { Middle Utica 
i Lower Utica 
r Probably Low- | 
I 
er Trenton 
Point Pleasant 
2. Diminution in Thickness of Utica, Lorraine, and Rich- 
mond southzvard. 
All of the major divisions and most of the subdivisions di- 
minish in thickness, from the more northern exposures in Ohio 
and Indiana, southward. In the case of the Utica, this di- 
minution in thickness cannot be established within the areas 
exposed in Ohio and Indiana ; however, the entire absence of 
the Utica in south-central Tennessee, in the area included be- 
tween Columbia, Centreville, and Franklin, suggests that this 
♦American Geologist, Oct., 1903. 
