fferent layers of
which are found the footmarks of long extinct birds. The beds in some
parts are twenty-five feet in thickness, composed of layer upon layer;
and on each of these layers, when horizontally split, are found
imprinted these remarkable footmarks. This result could only have been
produced by the subsidence of the ground, fresh depositions of sand
having taken place on the layers, on which the birds walked after the
subsidence. They must have been of various sizes,--some no larger than
a small sand-piper, while others, judging from their footprints, which
measure no less than nineteen inches, must have been twice the size of
the modern African ostrich. The distances between the smaller measure
only about three inches, but in the base of the largest, called the
Ornithichnites Gigas, they are from four to six feet apart. In some
places where the birds have congregated together none of the steps can
be distinctly traced, but at a short distance from this area the tracks
become more and more distinct. Upwards of two thousand such footprints
have been observed, made probably by nearly thirty distinct species of
birds, all indented on the upper surface of the strata, and only
exhibiting casts in relief on the under side of the beds which rested on
such indented surfaces. In other places the marks of rain and hail
which fell countless ages ago are clearly visible. Sir Charles Lyell
perceived similar footprints in the red mud in the Bay of Fundy, which
had just been formed by sandpipers; and on examining an inferior layer
of mud, formed several tides before, and covered up by fresh sand, he
discovered casts of impressions similar to those made on the last-formed
layer of mud. Near the footsteps he observed the mark of a single toe,
occurring occasionally, and quite isolated from the rest. It was
suggested to him that these marks were formed by waders, which, as they
fly near the ground, often let one leg hang down, so that the longest
toe touches the surface of the mud occasionally, leaving a single mark
of this kind. He brought away some slabs of the recently formed mud, in
order that naturalists who were sceptical as to the real origin of the
ancient fossil ornithichnites might compare the fossil products lately
formed with those referable to the feathered bipeds which preceded the
era of the ichthyosaurus and iguanodon.

THE BIG-BONE LICK.

We will now cross the Alleghanies westward, where we shall fi