170 F. B. Meek and A. H. Worthen on the Age 
by Prof. Hall to the Chemung group, placed it on a parallel with 
the Chemung, and Prof. Hall has also since referred equivalent 
beds in Iowa to the same horizon. 
In order that the reader may understand more clearly the po- 
sition of the Chouteau limestone with relation to our other west- 
ern formations, we give below a section showing the order of 
succession of the several beds, beginning with the Burlington 
limestone, which is acknowledged by all to be Carboniferous, 
and extending down to the Hamilton Group inclusive :— 
1.—Burlington limestone attaining a thickness of —- 200 feet. 
2.—Chouteau limestone, - - - - 100 “ 
3.—Vermicular sandstone and shale, - - 65 to 100 F 
60 
4.—Lithographic limestone (rather local), 
5.—Black Slate Cae - - 
, 30 to 40 ft.* | 
6.—Hamilton group, - - - 120 “ 
the beds below the Black slate. 
In regard to the occurrence of the Orthis which seems to be 
undistinguishable from O. Vanuxemi, in the Lithographic lime- 
stone, we would remark that we do not think it a en- 
titled to much weight, when it is borne in mind that 0. Van- 
uxemi is so very closely allied to the Carboniferous 0. Michr- 
lini of L’Eveille, that even Mr. Verneuil regarded them as 
scarcely distinguishable, and the differences between them have 
not yet been clearly defined. Prof. Hall acknowledges that 
it “is so closely allied to O. Michilini of L’Eveille, that 1b 8 
“ae Ky. and Indiana, the Black slate attains a thickness of about 
. fi 
