TF. H. S'udleston — On the Yorkshire Oolites. 121 



A complete and satisfactory answer to this question remains to be 

 discovered ; but there are one or two facts of great significance 

 which bear upon it. In the first place, we notice that there is no 

 connexion between the temperature at which a mineral separates 

 from a magma in which its constituents are held in solution, and 

 its own fusibility further than this — that no mineral can form at 

 a higher temperature than its own fusing point. Graphite, one 

 of the most infusible substances, crystallizes out of molten iron. 

 Quartz must constantly form at a point far below that of its own 

 fusibility. Then, again, there is the great question, first brought 

 into prominence by Scrope, as to the influence of water in determin- 

 ing the liquidity of lavas. Dr. Petersen has shown that the glassy 

 base of the Cheviot hypersthene-andesite is rich in water; the 

 devitrified base, on the other hand, is poor in water. 



The whole subject discussed in the last part of this paper is one 

 of great interest ; but we must be content to wait for a further 

 accumulation of facts before a perfectly definite judgment can 

 be formed. To those who collect and arrange these facts so as to 

 remove the subject from the region of controversy will belong the 

 chief merit of discovery. 



III. — Contributions to the Paleontology of the Yorkshires 



Oolites. 

 By Wilfrid H. Hudleston, M.A., F.E.S., F.G.S. 

 (Continued from Decade III. Vol. II. p. 69.) 

 (PLATE III.) 



' 74. — Trochus monilitecttjs, Phillips, 1829. Plate III. Figs. 1, 



la, 16. 



1829 and 1835. Trochus moniliteetiis, Bean ; Phillips, G T., p. 123 (p. 165 as 



T. moniliferus, P.), pi. ix. fig. 33. 

 1849. T. monilifectus, Phil. ; D'Orbigny,, Prod. p. 265. Et. Bajoc. 



1854. Ibid. Phil. ; Morr. Cat., p. 281. 



1875. Ibid. Bean ; Phillips, G. Y., 3rd ed. p. 259, pi. ix. fig. 33. 



Bibliography, etc. — This somewhat insignificant fossil approaches 

 several of the small granulated or tuberculated species of Trochus 

 (or Monodonta), which are distinguished by a completely conical 

 outline, resulting from a close suture and perfect flatness of the 

 whorls. Although without description, Phillips's figure is character- 

 istic, and it is somewhat singular that this species was not recognized 

 by D'Orbigny amongst the fossils of the French Jurassic. The 

 typical form is confined, in Yorkshire, so far as I know, to the 

 Scarborough Limestone (zone 3), where it is rare, and, for the most 

 part, so imperfectly preserved, that accurate description is a matter 

 of some difficulty. 



A single specimen referred to T. moniliteetiis from the Cornbrash 

 of Scarborough is in the Leckenby Collection. It presents certain 

 differences of ornamentation, and will be described as var. B. To 

 recognize a distinct species founded on a single specimen would be 

 imprudent, when the differences are not great. Should more specimens 



