very coarse sandstone,
were about thirtecn inches apart across the creature's chest, and rather
more than a foot apart from its fore to its hinder limbs. They were
alternately larger and smaller,--the smaller (those of the fore feet)
measuring about four inches in length, and the larger (those of the
hinder feet) about six inches. The number of toes seemed to be
alternately four and five; but from the circumstance that the original
matrix on which the tracks had been impressed,--a micaceous clay
resolved into a loose fissile sandstone,--had fallen away in the working
of the pit, leaving but the boldly-relieved though ill-defined casts on
the coarse sandstone, I could not definitely determine the point.
Enough, however, remained to show that at that spot,--little more than a
mile from where the Duke of Buccleuch's palace now stands,--large
reptiles had congregated in considerable numbers shortly after the great
eight feet coal seam of the Dalkeith basin had been formed. In another
part of the pit I found foot-tracks of apparently the same animal in
equal abundance, but still less distinct in their state of keeping. But
they bore testimony with the others to the comparative abundance of
reptilian life at an early period, when the coal-bearing strata of the
empire were little more than half deposited. It was not, however, until
the Permian and Triassic Systems had come to a close, and even the
earlier ages of the Oolitic System had passed away, that the class
received its fullest development in creation. And certainly very
wonderful was the development which it then did receive. Reptiles became
everywhere the lords and masters of this lower world. When any class of
the air-breathing vertebrates is very largely developed, we find it
taking possession of all the three old terrestrial elements,--earth,
air, and water. The human period, for instance, like that which
immediately preceded it, is peculiarly a period of mammals; and we find
the class, _free_, if I may so express myself, of the three elements,
disputing possession of the sea with the fishes, in its Cetaceans, its
seals, and its sea-lions, and of the air with the birds, in its numerous
genera of the bat family. Further, not until the great mammaliferous
period is fairly ushered in do either the bats or the whales make their
appearance in creation. Remains of Oolitic reptiles have been mistaken
in more than one instance for those of Cetacea; but it is now generally
h