FOOTPRINTS ON THE SANDS OF TIME 31 
interpretation of such evidences of ancient life has exercised the 
sagacity of naturalists since Dr. Duncan, in 1828, first inferred the 
existence of tortoises in certain sandstones in Dumfriesshire from 
the impressions left on them. The vast number and variety of 
such impressions has raised up a distinct branch of Palaeontology, 
to which the name Ichnology ^ has been given. 
We will now give a brief account of the results which have been 
arrived at in this branch of inquiry. To begin with one of the 
lowest forms of animal life — the worms. The class Annelida 
comprises the so-called ringed worms, including the leeches and 
earth-worms, and the sea-worms. As might have been expected, 
earth-worms are unknown in the geological record ; for their soft 
bodies were not likely to be preserved even in the most favourable 
kinds of deposits. But in some cases the hard jaws of marine 
worms have escaped destruction. Fossil worm-jaws are abundantly 
found in some parts of the Cambrian, Silurian, and Carboniferous 
systems (see Appendix I.). The so-called “ Conodonts ” are 
believed by many authorities to be the jaws of worms ; and such 
remains are also found in strata of the Mesozoic and Tertiary eras. 
Besides these rather mysterious little bodies, which some have 
taken to be the teeth of primitive fishes — such as our modern Hag- 
fish, — a good many worm-like markings are found in muddy and 
sandy sediments all through the stratified series. In many cases 
the true nature of these remains is still a matter of doubt. The 
visitor to the Natural History Museum at South Kensington will 
find in Gallery No. XI. a very fine and large collection of fossil 
tracks and footmarks of all kinds (Wall-cases Nos. 8-12). Some 
of these are probably vegetable remains ; but others are certainly 
the tracks of molluscs or of crustaceans. Long burrows of marine 
worms occur plentifully in some rocks of Cambrian and Silurian 
^ Greek — dchnost footstep ; logos, discourse. 
