Human Foot-Prints in Solid Limestone. 19 
There is but one corroborative, though not essential evidence, 
desirable to add to that already given in proof of the age of this 
rock. ‘The uppermost bed of the group to which it belongs is a 
stratum of limestone of a reddish tint, and characterized by a 
very remarkable fossil coralline, resembling the Retepora of Lin., 
but verticillated spirally like a continuous screw ; described by 
Lesueur under the appropriate name of Archimedes.* Here is a 
sketch (Fig. 2) of one in my possession : . 
Archimedes, of Lesueur. 
In the same rock which contains this fossil, or in the beds im- 
mediately beneath it, which often exhibit an oolitic structure, the 
* I am not sure that Lesueur ever published his description of this fossil; but I 
know that while he resided here (at New Harmony) he engraved a plate contain- 
img several views of it, with that intention. He considered it, 1 believe, a new 
genus ; but’it ma 1? be as anew species of Retepora; if so, most aptly entitled 
Retepora Archi 
