ft of the longer turtle-track,
near the largest bird-track; the second is on the track; the third is
above the track; the others cross the slab by fainter impressions.
Each of them is composed by two feet, and each foot contains four
toes, which are seen more distinctly in some impressions than in
others. The largest of these double tracks is about three inches in
diameter. Perhaps it would be useless to speculate upon what kind of
animal they were made by. There is a similarity between these and the
tracks of the Anomoepus Scambus, spoken of in the sixth group. In the
latter, however, the toes are five and three. Some experienced persons
think they are tracks of the mink, Mustela Lutreola, an animal common
at the present day in these parts. This has five toes; but it may be
in this as in some other digitigrades, that one of the toes in each
foot does not make an impression; or perhaps it is safer to believe,
till further investigation is made, that it was an animal of a
construction not now existing.

The direction of these tracks presents a puzzle we are not able to
unravel; it exhibits the impressions of four toes, and we have
supposed it might possess five. In either of these cases, we have no
right to consider it a bird-track, but probably a reptile or a mammal.
Admitting this to be the fact, we are unable to account for the
direction of the steps, which is not alternate, as in the quadruped,
but in straight lines. In other words, this animal, supposed to have
four legs, gives us the impressions of two only, and both of these
placed together.

When the tridactylous tracks are attentively considered, compared with
each other, and with the digitated tracks, they appear to exhibit the
character of the impressions of the feet of birds so very decidedly,
that it would require something more than a philosophic incredulity to
question their ornithic origin.

The other side of this slab contains interesting impressions. In the
first place, this surface is covered with ripple-marks, each about two
inches broad, extending with various degrees of distinctness across
the slab, and having an interval of an inch. The width of the ridges
is greater than in any of the specimens we have seen.

This surface is almost covered by rain-drops. It has also, among other
impressions, one which has been drawn by Mr. Silsbee, our
photographist, and represented by the figure below of its proper size.
This figure, nearly four and a half i