Since writing the preceding article, I have been able to obtain,
through the kindness of President Hitchcock, a number of additional
specimens of fossil impressions. By the aid of these, I may hope to
give an idea of the system of impressions, so far as it has been
discovered, without, however, attempting to enter into minute details.
For these, I would refer to the account of the "Geology of
Massachusetts," by President Hitchcock; to his valuable article
published in the "Memoirs of the American Academy;" and to his
geological works generally.
The numerous tracks which have been assembled together in the
neighborhood of Connecticut River have afforded an opportunity of
prosecuting these studies to an extent unusual in the primitive rocky
soil of New England. These appearances are not, indeed, wholly new.
Such traces had been previously met with in other countries; but, in
their number and variety, the valley of the Connecticut abounds above
all places hitherto investigated.
Twenty years have elapsed since the study of Ichnology has been
prosecuted in this country; and, in this period of time, about
forty-nine species of animal tracks have been distinguished in the
locality mentioned, according to President Hitchcock; which have been
regularly arranged by him in groups, genera, and species.
I propose now to lay the specimens, recently obtained, before the
Society, as a slight preparation for the more numerous and more
valuable articles which they are soon to receive.
The traces found on ancient rocks, as has been shown in the previous
article, are those of animals, vegetables, and unorganized substances.
The traces of animals are produced by quadrupeds, birds, lizards,
turtles, frogs, mollusca, worms, crustacea, and zoophytes. These
impressions are of various forms: some of them simple excavations;
some lines, either straight or curved, and others complicated into
various figures.
President Hitchcock has based his distinctions of fossil animal
impressions on the following characters, viz.:--
1. Toes thick, pachydactylous; or thin, leptodactylous.
2. Feet winged.
3. Number of toes from two to five, inclusive.
4. Absolute and relative length of the toes.
5. Divarication of the lateral toes.
6. Angle made by the inner and middle, outer and middle toes.
7. Projection of the middle beyond the lateral toes.
8. Distance between tips of lateral toes.
9. Distance between tips of middle and inner and outer toes.
10. Position and direction of hind toe.
11. Character of claw.
12. Width of toes.
13. Number and length of phalangeal expansions.
14. Character of the heel.
15. Irregularities of under side of foot.
16. Versed sine of curvature of toes.
17. Angle of axis of foot with line of direction.
18. Distance of posterior part of the foot from line of direction.
19. Length of step.
20. Size of foot.
21. Character of the integuments of the foot.
22. Coprolites.
23. Means of distinguishing bipedal from quadrupedal tracks.
By these characters, President Hitchcock has distinguished
physiological tracks, or those made by animated beings, into ten
groups provisionally. To these may be added, "organic impressions,"
made by organized bodies; and the impressions made by inanimate
bodies, called "physical impressions."
The specimens under our hands enable us to give some notion of the
distinctions which characterize the greater part of these groups.
* * * * *