Human Foot-Prints in Solid Limestone. 21 
The whole Pentremital series is a remarkably pure variety of 
limestone. . A quantitative analysis of a portion of the slab. in 
which the foot-prints occur, gave the following result ; 
hs a acid, . eee why eee . 40.80 grains, 
8.80 
A Mags : . ; : ‘ : ee 60 
si lica . . . . . . 2.00 
Oxide of iron and loss, ; ; ‘ i» 26,80: 
ss 00 gis... 
Specific gravity, : 67 
The color of the slab ” not to quite sai given by 
Schoolcraft. He describes it as of a “grayish blue tint ;” but, 
on the exposed and worn surface, it has rather a purple tint ; and, 
when fractured, is of a very light gray. I mention this oe 
the blue tint is by no means characteristic of this group of lime- 
stones, but is peculiar to the lowest limestones of the Ohio valley, 
considered the equivalent of the lower Silurian rocks of Murchison, 
and the Salmon river and Trenton rocks of New York, and on 
account of this prevailing tint, frequently described as the “blue 
fossiliferous limestones.” They lie from eight hundred to one 
thousand feet lower in the geological series than the Pentremital 
limestones now under consideration. 
So much for the age of the rock in which these foot-prints are 
found. The question nett, presents itself, are they true fossils, 
or are they the work of art 
: ition. of this question, I have given (in the 
this a } representation of the 
the present ap- 
rs since it has been quar- 
. cy f , Pokaan A oe seems t 
ried, no material or apy ble alteration to have occurred,* 
* Nor does it appear that these impressions had changed in appearance while 
the rock was in situ, I quote from the letter of Col. Benton (an eye witness) to 
Mr. Schoofcraft, referred to in the extracts hereinafter given from the latter gen- 
tleman’s article : 
‘The prints were seen when the country was first settled, and had the same 
pone then as now. No tradition can tell any thing abet them. They look 
as 0] ; they bave the same fine polish which the attrition of the sand 
’ 
