Mr. A. Hancock on Vermiform Fossils. 455 



crustaceans ; it therefore only remains to be ascertained whether 

 thejr can be attributed to any known fossil of the Carboniferous 

 rocks. 



j\Ir. Howse has suggested to me that they may be the runs of 

 Trilobites, several species of which occur in this formation. This 

 is not by any means unlikely. It is true, I believe, that these 

 curious crustaceans have never been found in the rocks in which 

 these tracks occur. They are most abundant in the lower mem- 

 bers of the Carboniferous system, though they occasionally 

 occur higher up in the series. Professor Phillips, in his work 

 on the ' !>Iountain Limestone District of Yorkshire,' gives Alston 

 Moor as one of the localities of Asaphus yemmuliferus ; and I 

 am informed by Mr. Howse that he has obtained in Tynedale 

 two or three specimens of a Trilobite from a plate bed a little 

 above the Scar limestone of Forster's section ; and he further 

 states that the Yoredale rocks correspond exactly to the Wear- 

 dale series above Stanhope, that is, from the little limestone to 

 the Scar limestone, and that the specimens of tracks procured 

 in Weardalc are from the slaty Hash immediately above the 

 latter — a position agreeing with that of the beds in the neigh- 

 bourhood of Howes. The tracks from Haltwhistle are, he like- 

 wise states, from a slaty Hash just above the little limestone. 



It is therefore of no great moment that Trilobites have not 

 been found in the strata from which these v'ermiform fossils are 

 obtained, since they have been procured from the associated 

 beds. And it is a remarkable fact that no remains whatever of 

 any organic body are found in these flagstones ; yet is there not 

 sufficient evidence to prove that life abounded in the seas from 

 which these rocks were derived ? Numerous Trilobites might 

 have existed during their deposition, and may have perished 

 with the other inhabitants of those seas, lea^dng no trace behind 

 them, except these, as it were, footprints in the sand. Many 

 such footprints are all that is left in the world's stony record of 

 existences that have passed away j and so it may be with these 

 fossil tracks. 



The Carboniferous Trilobites, however, correspond very well in 

 size to the tracks, the largest of the grooved kind of which, we 

 have seen, is a little above an inch wide. The width of the 

 pygidium of Phillipsia truncaiula is stated to be eleven lines, — 

 that of the cephalic shield would probably be a httle more; 

 therefore, if allowance be made for the thickness of the tunnel- 

 wall, and the necessary enlargement of the calibre beyond the 

 width of the animal, it is evident that, so far as size is concerned, 

 the largest tracks might be attributed to this species. 



The nodulous tracks are not more than half an inch wide; 

 there can therefore be no difficulty as to size with respect to 



31* 



