92 The America?} Geologist. August, isse 
Cherty bed of the Keokuk Limestone. 
Knobstone^of Ind.| Knobstone 
WaveTly of Ohio )■ Grey shales. 
Chouteau of Mo. J ■ -^ 
Devonian Genesee shale. 
Section of Knobs of Bullitt, Marion, and Boyle counties. 
Kentucky. 
b. The Ki'oliuh Limestone. 
or Lower Archimedes limestone proper of Owen, is best exposed 
at Keokuk, overlying the cherty beds forming the rapids, and at- 
tains a thickness of forty feet. This bed gradually thins out 
toward the north and at its edges consists of alternations of argil- 
laceous and arenaceous beds with subordinate beds of encrinital 
limestone. This character is seen to the extreme in the neigh- 
borhood of Mount Pleasant, Iowa, and at a less degree at Ap- 
panoose, Illinois. In Missouri the bed is exposed at Hannibal 
and at Boonville, cliffs of this limestone with its overlying equiv- 
alent of Magnesian division can lie traced from the mouth of 
Riviere la Mine to below the town, forming a series of wave-like 
anticlinal axes. The following section was observed: 
Chert in irregular beds interstratified with beds of shaly limestone 
and calcareous clay, equivalent of the Magnesian limestone of Owen 
and the Warsaw of Hall — 3 to 6 feet. 
Hard blue limestone, containing Productus nvigrms, P. seini-reticuhitus, 
p. punctfitus and Archimedes owenann. The Keokuk or Lower Archi- 
medes limestone proper— 30 feet. 
In Illinois this division of the Keokuk forms the heavy cjuarr}- 
rock at Hamilton, Nauvoo, Niota and Quincy. In Indiana the 
only equivalent is found on south branch of Walnut Fork in 
Montgomery county, the following is a section of the rocks: 
Poil 10 to 20 feet 
Blue shale — containing small pockets of crinoida 5 " 
Heavy quarry Lmestone, containing characteris- 
tic "fossils — seen in the bottom of the creek. . .2 to — " 
In Kentucky the writer has been unable to distinguish this 
division at any outcrops visited. 
c. Thr Grodc Bed. 
This may be found resting upon the Keokuk limestone proper 
at Keokuk, consisting of a bed of forty feet of calcareous shale 
or marl, containing numerous geodes of quartz and chalcedony 
