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 l 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 L). 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 

 1 Greek ichnos, footstep ; logos, discourse. 



