408 Keokuk Group at Craw fords ville^ Ind. — Beachhr. 
Feet. 
Sandstone, containing fossils 30 
Blue shale, crinoid beds 5 
Limestone, encrinal 2 
Blue shale, containing fossils 25 
62 
The Keokuk series is wholly of marine origin, this being de- 
termined by the remains of plants and animals, the plants be- 
ing fucoids and the animals being corals, crinoids and marine 
shells. The overlying arenaceous rock in places, marks dis- 
tinctly the wave action of the sea. In the argillaceous and 
calcareous rock the lamination is regular and generally thin, 
the intervals of quiet being marked by the massive beds. 
The horizontal position of the strata was assumed in obedi- 
ence to the law of gravity; and after elevation parallel with the 
Cincinnati anticlinal, the variation was slight, dipping toward 
the west. 
The "geode bed" which forms the upper series of the group 
in Iowa and western Illinois, is wanting at this locality; the 
fifty feet of regular bedded calcareous rock exposed at Keo- 
kuk, Iowa and Nauvoo, Illinois is represented at this locality 
by fifty feet of arenaceous and argillaceous rocks; the lowest 
series of the group, consisting of clierty limestone and forming 
the transition beds between the Keokuk and Burlington groups 
is also wanting at this locality. 
It will be seen from the above facts that the Keokuk lime- 
stone on the west border of the central coal field, becomes 
arenaceous on the east. 
The Keokuk group, like all of the Sub-carboniferous forma- 
tions, thins out and disappears east of this locality. 
The characteristic fossils of this formation are the Agari- 
cocrinus americanus, Forbes locrinus meeki with several other 
species of crinoidea peculiar to this locality; and these are as- 
sociated with Platyceras equ/'lafera, P. sub-rectum, Archimedes 
owenana, Spirifer cuspidatw? and S. sub-orbicularis, which 
clearly establish the true horizon of these shales and sand- 
stones as stratigraphical equivalents of the Keokuk limestone 
of Illinois and Iowa.* 
It might be well to add here the species Productus magnus 
*Geol. Rep. 111., vol. i, p. 101. 
