ON CERTAIN VERMIFORM FOSSILS. 31 



This seems a pretty conclusive proof tliat this large vermiform 

 fossil is not a worm-tube or any organic body, but is really 

 nothing more than a track which was, in fact, originally, as it is 

 now, composed of the same material as the slab upon which it 

 rests, or the appearances as above described could not exist. 



There still remains another very conclusive argument against 

 the organic nature of these fossils. The folds or windings of 

 both the grooved and nodulous forms occasionally cross each 

 other, and when they do so, the one does not lie over the other, 

 as it must necessarily have done were they organic, but passes 

 right through it, cutting its own path (PI. VII. h). This is still 

 more clearly demonstrated in the fine large specimen of the no- 

 dulous form previously alluded to (PI. V. 6, &), and appears only 

 explicable on the hypothesis of their being mere tracks; and 

 perhaps it will now be allowed that enough has been said to 

 establish the high probability, at least, that they were formed by 

 crustaceans. It therefore only remains to be ascertained if they 

 can be attributed to any known fossil of the carboniferous rocks. 



Mr. Howse has suggested to me that they may be the runs of 

 trilobites, several species of which are obtained from this forma- 

 tion. 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 

 members of the carboniferous system, though they occasionally 

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

 on the " Mountain Limestone Districts of Yorkshire," gives 

 Alston Moor as one of the localities of Ascqjlms gemmuliferus ; 

 and I am informed by Mr. Howse, that he has obtained in TyncT 

 dale 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 

 Weardale series above Stanhope, that is, from the little limestone 

 to the scar limestone, and that the specimens of tracks procured 

 in Weardale are from the slaty hazle immediately above the 

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

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



