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, in a rock, the exact 

 geological position of which I had already satisfactorily ascer- 

 tained. This stratum hes 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.) 



Fig. 1. 







Producta found in the slab. 



In the above plate, a a are the under and npper valves of a 

 species which I have not seen described ; b b represent the exter- 

 nal and internal view of the under valve of another species, also, 

 I believe, undescribed ; nor have I seen d described ; c resembles 

 the Producta Martini of Soto., but its under valve is much flat- 

 ter and less distinctly striated. 



I had 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 ; but I 

 had not had an opportunity, during extreme low water, of making 

 a thorough examination at that place. The discovery of these 

 Producta confirms in a satisfactory manner my previous views. 



