JONES — TRAILS, TRACKS, AND SURFACE-MARKINGS. 



131 



marked footprint, and that it was of earlier date is shown by one ot 

 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 ot 

 the iirst-mentioued track. 



Specimens of sandstone showing the casts of similar convex and 

 concave trails are common in some of the Wealden beds * 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 {Sideator 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. 



Ur. 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, 201 ; Quart. Jour. Geol. Soc, vol. x. p. 208 ; xii. p. 216 ; 

 xiii. p. 199, etc. In these instances, Fishes, Crustaceans, Molluscs, 

 and Worms have been quoted as the probable agents. 



In his ' Eeport on the Agriculture of New York' (' Natural History 

 of New York,' Part Y.), vol. i. (1816), p. 68, etc., plates 14, 15, 16, 

 Professor E. Emmons describes and figures several so-called Lower 

 Palseozoic "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 'Paleontology of New York,' 1852, vol. ii. p. 26, etc.; and 

 numerous figures of such and other surface-markings from the Silu- 

 rian rocks of the State of New York are given in the plates 11 to 16 of 

 that volume. t Indeed, of the so-called Eucoids illustrated by plates 

 1, 2, 3, 5, 5^ 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 

 JS'emajpodia tenuissima of Emmons has been proved to be the trail ot 

 some existing animal over the outer surface of the rock, removing the 

 minute licheu which covers it, and discolouring the rock beneath." — 

 J. Hall, Palseont. New York, vol. ii. p. 32, note. 



An instance in which recent tracks have been figured in illustration 



* On the under-siirface of a rippled sandstone shale from Staramerham, near Horsham, 

 I have observed numerous small, tliread-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. 



t Notes by the late Prof. E. Forbes, ou some of these figures, are appended by Mr. J. 

 Hall, at page 37. 



