396 Foot-prints of Birds and Impressions of Rain-drops. 
upwards into the very flags on which Ornithichnites occur; and from 
this he infers, that there were eruptions of trap, accompanied by up- 
heaval and partial denudation, during the deposition of the red sandstone. 
With respect to the impressions having been made by birds, Mr. Ly- 
ell states, that until he examined the whole of the evidence he enter- 
tained some scepticism, notwithstanding the luminous account given by 
Prof. Hitchcock. In proof of their being the foot-prints of some crea- 
ture walking on mud or sand, he mentions, Ist, the fact of Prof. Hitch- 
cock’s having. seen two thousand impressions, all, like those he had 
himself examined, indented in the upper surface of the layer, the casts 
in relief being always on the lower surface ; and 2dly, that where there 
is a single line of impressions, the marks are uniform in size, and near- 
ly uniform in distance from each other, the toes in the successive steps 
turning alternately right and left. Such single lines, Mr. Lyell says, 
indicate that the animal was a biped, and the trifid marks resemble those 
which a bird leaves, there being generally a deviation from a straight 
line in any three successive prints; and his attention having been call- 
ed to indications of joints in the different toes, he afterwards clearly re- 
cognized similar markings in the recent steps of coots and other birds 
on the sands of the shores of Massachusetts. Prof. Hitchcock has 
shown, that the same impression extends through several laminz, de- 
creasing in distinctness in proportion as the layer recedes from that in 
which it is most strongly marked, or in proportion as the sediment fill- 
ed up the hollows and restored the surface to a level; and Mr. Lyell 
states, that he has observed a great number of instances of this fact. 
He also says, that he can scarcely doubt that some of the impres- 
sions on the red sandstone of Connecticut are not referable to birds, 
but he believes that the gigantic ones described by Prof. Hitchcock are 
Ornithichnites. At Smith’s Ferry they are so numerous that a bed of 
shale many yards square is trodden into a most irregular and jagged 
surface, so that there is not a trace of a distinct footstep; but on with- 
drawing from this area to spots where the same tracks are fewer, the 
observer, Mr. Lyell says, is forced to admit that the effect in each case 
has been produced by this cause. 
On examining the shores on some small islands about fifteen miles 
southeast from Savannah, the author was struck with the number as 
well as the clearness of the tracks of raccoons and opossums imprinted 
in the mud during the four preceding hours, or after the tide had begun 
to ebb. At one spot, where the raccoons had been attracted by the oys- 
ters, the impressions were as confused as when a flock of sheep has 
passed over a muddy road; and in consequence of a gentle breeze 
blowing parallel to the line of cliffs composed of quartzose sand, the 
tracks had in many places already become half filled with blown sand, 
