reat, novel, and
interesting.

This inquiry seems to us to promise a rich variety; and we hope that
President Hitchcock and other observers will continue to explore and
cultivate it with undiminished zeal.

DESCRIPTION OF THE PLATE.

We are indebted to Photography for enabling us to represent the
remarkable slab from Greenfield, and its numerous objects, in a small
space, yet with perfect accuracy. This slab is four feet seven and
one-half inches in one direction, and four feet one inch transversely
to this; in thickness it measures about an inch. It is composed of
gray sandstone, in which the micaceous element is conspicuous, and
contains many interesting impressions on both surfaces.

The most interesting surface is the inferior; and the objects are, of
course, presented in relief. They are, first, two Chelonian tracks;
second, four sets of bird-tracks; third, footsteps of an unknown
animal. The _Chelonian tracks_ are two in number: the longest measures
four feet ten inches; the shorter, two feet nine inches. Both of these
impressions are made apparently by the plastron of the turtle. They
are from four to eight inches in width, and composed of elevated
striae. These striae are formed by raised lines, pursuing a course
generally regular, but accompanied with some inflections: they are, as
the plate represents, very distinct. The shorter track appeared to me
to be crossed by another; but the photographic impression, though only
a few inches long, enabled me to ascertain that this appearance was
produced by bird-tracks above and below.

The _bird-tracks_ are all tridactylous. The first set lies above and
to the right of the shorter turtle-track, and is composed of only two
steps, proceeding in the course of the plate downwards. The second set
of bird-tracks has five impressions, extending from the right superior
pointed angle of the slab across the small turtle-track to the larger,
in which it is lost. The third set of bird-tracks begins by an
impression larger than any other on the piece at the left extremity of
the longer turtle-track; and the remainder, three in number,
descending towards the right, are the least distinct of any. The
fourth set of bird-tracks begins below the longer turtle-track, and
ascends by four impressions, crossing the track till it meets the
first.

The most curious track, consisting of six digitated impressions, still
remains. The first is seen on the le