marked footprint, and that it was of earlier date is shown by one of the gallery-marks passing athwart one of its toe-prints, whilst the other end of the gallery has been trodden in by the last foot-mark of the first-mentioned track.
Specimens of sandstone showing the casts of similar convex and concave trails are common in some of the Wealden beds[1] and other thin-bedded rocks formed in shallow water ; but the modifications are extremely numerous, and will require much careful observation before they are elucidated. Accurate drawings, at least, should be taken of trails and other surface-markings made by aquatic animals. Mr. A. Hancock's published sketches (above referred to) of the gallery-tracks of minute crustaceans (Sulcator arenarius and Kroeyera arenaria) that bore the sand of the sea-shore, are good examples of what is required of those who would assist the geologist to decipher the obscure tracks and trails (too often termed annelid-marks) by the light of nature.
Mr. Poulett-Scrope, Mr. Strickland, Dr. Buckland, and Mr. Salter have published the results of some careful comparisons of recent and fossil tracks and trails; but have not figured the recent markings on which their conclusions rest. See Geol. Proceed., vol. i. p. 317; iv. pp. 16, 204; Quart. Jour. Geol. Soc., vol. x. p. 208; xii. p. 246; xiii. p. 199, etc. In these instances, Fishes, Crustaceans, Molluscs, and Worms have been quoted as the probable agents.
In his 'Report on the Agriculture of New York' ('Natural History of New York,' Part V.), vol. i. (1846), p. 68, etc., plates 14, 15, 16, Professor E. Emmons describes and figures several so-called Lower Palæozoic "annelid-tracks," such as he has since referred to the trails of larval insects.
Some sagacious remarks on fossil trail-prints are made in Mr. James Hall's 'Palæontology of New York,' 1852, vol. ii. p. 26, etc.; and numerous figures of such and other surface-markings from the Silurian rocks of the State of New York are given in the plates 11 to 16 of that volume.[2] Indeed, of the so-called Fucoids illustrated by plates 1, 2, 3, 5, 5a, 6, 7, 8, 9, and 10 of that volume, there are some that have been referred by Mr. Salter to the work of Annelides. Mr. Hall says—"As a fact in proof of the similarity of the trails of other animals to these supposed remains of Annelida, I may mention that the Nemapodia tenuissima of Emmons has been proved to be the trail of some existing animal over the outer surface of the rock, removing the minute lichen which covers it, and discolouring the rock beneath."—J. Hall, Palæont. New York, vol. ii. p. 32, note.
An instance in which recent tracks have been figured in illustration
- ↑ On the under-surface of a rippled sandstone shale from Stammerham, near Horsham, I have observed numerous small, thread-like cylinders of sandstone, forming an irregular reticulation, which must have been due to the fine sand, when moist, having entered horizontal galleries in a clay or mud beneath: after having hardened, the sand, on the removal of the clay, has remained in the form of delicate free cylindrical casts, attached by their ends to the under-surface of the slab.
- ↑ Notes by the late Prof. E. Forbes, on some of these figures, are appended by Mr. J. Hall, at page 37.
