182 Ornithichnites of the Connecticut River Sandstones. 
marks of organization are traced with great fidelity. ‘There are 
no conflicting phenomena to disturb the inevitable conclusions of 
the judgment, but a mutual relation is ever perceptible, that carries 
the internal evidence that these marvellous impressions are the gen- 
uine vestiges of birds, and that no quadruped animal with which 
we are acquainted, living or extinct, would have made them. 
The feet of birds being so prominent an organ, to separate them 
into generic divisions, we cannot omit to inquire if the extinct 
genera have their representatives in the living. The inference 
is that by leaving their traces on the muddy bottoms and margins 
of the ancient waters, the extinct birds were waders, and to some 
of the species the classification of living birds supplies a simili- 
tude. ‘The O. tuberosus is very accurately represented so far as 
form is concerned, by the pinnated feet of the Fwlica custata and 
other genera of the order Grallz, the toes being bordered by 
membranes that give the same form and expression to the foot, 
and completes the presumption that these remarkable imprints 
are authentic traces of birds. 
Assuming them to be such, the enquiry naturally suggests 
itself why we do not discover the co-existence of these fossil 
bones; but there are plausible explanations why the skeletons of 
birds should not be found in strata deposited by the agency of 
water. It is not the element in which birds live, and as nature 
in her appointments has adapted all animals to the media in 
which they exist, we may see in this law a philosophical reason 
why their bones do not exist. 'The osseous system of birds con- 
sists merely of thin cylindrical shells of great strength and buoy- 
ancy, and it therefore results that should death accidentally hap- 
pen upon water, the carcass would not be quietly deposited at the 
bottom, but be drifted about by currents until destroyed by de- 
composition or violence. This seems to be a legitimate conclu- 
sion, although it by no means follows that such bodies would not 
accidentally become entangled at the bottom, or be suddenly en- 
veloped by a stratum of that plastic material subsequently to be 
converted into solid rock. It is not therefore impossible but the 
skeleton may be discovered, a single bone of which will be suffi- 
cient to determine the order of animals to which it belongs. And 
if comparative science be so invariable in its application, that 
from a fragment a complete fabric may be restored, does it not 
follow with great force, that from exact impressions of each bone 
