TF, H. Hudleston — On the Yorkshire Oolites. 61 



The Dogger Sands and the Dogger are the most prolific in forms, 

 and also in individual specimens, the mitrz'catou-gi'oup, as we shall 

 see, being fairly well represented and of considerable variety, more 

 especially in the Dogger Sands,^ where, if we may judge from 

 numerous specimens in the Leckenby Collection, there has been 

 considerable tendency to change. 



22 and 23. — Cerithium muricatum group, Sowerby, 1825. PI. III. 



Figs. 1—8. 



182-5. Turritella muricata, Sow., Min. Couch., vol. v. p. 159, pi. 499, figs. 1 and 2. 



1829. ,, ,, „ Phillips, G. T. 1st edition, p. 164. 



1831. Cerithium echinatum, Von Buch, Jura in Deutschland, p. 56. 



1836. Cerithium quadriiineatum, Rom. (pars), Ool. Geb. p. 154, pi. 11, fig. 14. 



1844. Cerithium granulato-costatum and mwicato-costatum, Miinst. (pars), Goldf. 



pi. 173, figs. 10 and 12. 



1875. Cerithium muricatum, Sow. ; Phillips, G. Y. 3rd edition, p. 258. 



Bibliography, etc. — As previously intimated, C. muricatum, Sow., 

 is to be regarded as a group, rather than as a species in an ordinary 

 sense — a group in fact out of which perhaps more than half the 

 species of Cerithia that figure in the lists from the Lower and part 

 of the Middle Oolites has been carved. In dealing with the shells 

 which are classed imder this heading the paleeontologist's dilemma 

 presents itself with unusual force. Are all the forms which exhibit 

 some slight divergence of ornament or proportions to enjoy full 

 specific distinction? This primary difficulty is further complicated 

 by others, of which the difference in appearance, due to diversity of 

 mineralization thoughout the seven zones, is very grievous, and one 

 that especially affects all highl}' sculptured forms. 



In this case, however, there is a fiirther and special difficulty — no 

 less, in fact, than the crucial question, what is the type ? Sowerby 

 appears to have had no doubt that the Steeple Ashton fossil was 

 identical with that from the Dogger of the Peak (Blue Wyke), and 

 Phillips, in the earlier editions of the Geology of the Yorkshire 

 Coast, evidently took the same view, since he quotes Turritella muri- 

 cata as occurring in the Coralline Oolite, Lower Calcareous Grit, 

 Kelloway Rock, and Dogger. In the last edition (1875) Phillips 

 quotes Cerithium muricatum from the Coralline Oolite, Lower Cal- 

 careous Grit, and Cornbrash only. Its occurrence in the Dogger is 

 not alluded to in any way, nor is there any alternative name given 



1 It should be borne in mind that the Dogger Sands are classed as part of the 

 Upper Lias by some authorities, though not by Tate and Blake, who enumerate 

 eiglit species of Cerithium from the entire formation, not including these Sands. 

 Again, the division between the Dogger and the Dogger Sands at Blue Wyke may 

 be drawn somewhat differently. This subject has been discussed by me at some 

 length in the first part of the " Yorkshire Oolites " (Proc. Geol. Assoc, vol. iii.), 

 where it was pointed out that, besides the iVrt-«w««-bed which }ields the bulk of the 

 specimens classed as "from the Dogger," there are three fossiliferous beds below 

 this which form a part of the Dogger proper. The irony condition of the Nerincea- 

 bed and its shells is generally a pretty safe test as to a specimen coming from the 

 Dogger, but this is not in all cases to be relied upon as regards the lower fossiliferous 

 zones, which yet form part of the Dogger and not of the Dogger Sands. Hence 

 there is a possibility in some cases that fossils believed, on account of their matrix 

 and mineral condition, to have come from the Sands, may in reality have been 

 obtained from the lower fossiliferous beds of the Dogger proper. 



