4 
ON THE FOSSIL FOOT-MARKS 
These consisted of some of the same kind of “ foot-prints, with others of a very different 
form, and these were accompanied by more perfect specimens of impressions of plants than 
had before been discovered. These were of great interest, as their structure indicated 
their being “air plants.” The Professor named them Plumites. He also mentioned that 
he had found Stigmaria in the “ red shale ” of formation No. 11. Prof. Agassiz subse¬ 
quently remarked on these tracks, and objected to any of them being considered as made 
by “reptiles.” He did not believe that any of them were made by air-breathing animals; 
that these “ trails ” could not be made by “reptiles” but that they must have been made 
by “ annilids or fish,” and most probably by “ Articulata .” He farther stated that in his 
belief no air-breathing animal had been found even as low as the New Red Sandstone. 
Without disputing such authority as that of Prof. Agassiz, I shall hold to my own 
opinions, as expressed in my former communication, as to the fact of these “ foot-marks ” 
being impressed by a four-footed, air-breathing animal, allied to the “Saurians,” having 
four toes on the hind foot and five on the fore foot. As regards the opinion of there 
having been no air-breathing animals in existence as low as the New Red Sandstone, it 
appears to me to be fully answered in the negative by the existence of the Chirotherium , 
(Lahjrinthodon , Owen,) Thecodontosaurus , &c., in that formation in Europe, and by the 
recent discovery of the bones and teeth of a Sauroid animal in the New Red Sandstone 
of Lehigh county, Penna., announced by me in the Proceedings of the Academy of 
Natural Sciences, last year, and which I named Clepsysaurus Pennsylvanicus. 
As regards the observation of Prof. Rogers, that the “ foot-prints ” at Mount Carbon 
were “of an age essentially later than that attributed to them” by me, I would reassert 
that what I then stated was correct, that is, that they existed in his “ red shale formation,” 
No. 11, of his Pennsylvania survey. There is no error, as implied by Prof. Rogers’ 
communication, in this fact; the position of the “foot-marks” is undeniable. The differ¬ 
ence is simply whether formation No. 11 be part of the “ Old Red Sandstone formation ” or 
not. It was my opinion, with that of most of our geologists, that in the Pennsylvania 
Reports, when the term “red shale formation,” No. 11, was used to designate a “period” 
two “ formations” below the coal measures, (For. 13,) the Old Red Sandstone, analogous to 
that of Europe, was considered to be understood.* The late Richard C. Taylor, whose 
authority, on the geology of this state was inferior to none other, was said by Prof. Silli- 
man, Mr. Hall and others, to have been the first person in this country who had referred 
the Old Red Sandstone underlying the coal of this state, to its true position, correspond- 
* The position of Prof. Rogers’ “red shale formation,” (No. 11,) is thus described by him:—“A very brief 
description will, for the present, suffice to designate the range of the red shale formation. Encircling in a con¬ 
tinuous zone all the anthracite coal basins of the state, it usually constitutes a chain of deep and narrow valleys 
enclosed between the ridges of Formation No. X. on the one side, and on the other, those containing Formation 
No. XII., composing the margin of the coal measures.” 
“The maximum thickness of this formation occurs, apparently, in its south-eastern belt, or that which ranges 
along the south side of the southern anthracite coal basin. From accurately conducted measurements made at 
Pottsville, the depth of the stratum at that place is about 2,949 feet.”— Second An. Report, p. 66. 
“ Formation No. XII.” he designates as “conglomerates and sandstones immediately below the coal measures 
of the Anthracite, the Broad Top and the Allegheny coal regions,” which, at Pottsville, he makes 1031 feet. 
