= a thorough e 
18 Human Foot-Prints in Solid Limestone. 
portion into small hand specimens. I was thus enabled definitely 
to determine the age of the rock. 
The fossils obtained, proved on examination to be the same ~ 
species which I had often previously observed at Leavenworth 
in Indiana, on the Ohio river, and elsewhere, ina rock, the exact 
geological position of which I had already satisfactorily ascer- 
tained. This stratum lies from ten to twenty feet below the 
lowest members of our true coal measures, and is considered the 
equivalent of the mountain limestone of Europe. 
Four species of Producta, the best preserved among those ob- 
tained from the slab, are:here represented, (Fig. 1.) 
Producta found in the slab. 
In the above plate, aa@.are the under and upper valves of a 
species which I have not seen described ; .b 6 represent the exter- 
nal and internal view of the under valve of another species, also, 
A believe, undescribed ; nor-have I seen d described ; ¢ resembles 
the Producta Martini of Sow., but its under valve is much flat- 
ter and less distinctly striated. 
Thad long since felt assured, from the bearings of our geolo- 
gical formations, that the limestone of which these are character- 
istic fossils, formed the bed of the Mississippi at St. Louis; bu 
had not had an opportunity, during extreme low water, of 
amination at that place. The discovery 
Producta confirms in a satisfactory manner my Piste riew 
FA 
oe 
MN cds Dan 
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“a 
