part 4] 



JURASSIC CHROlSrOLOGY. 



419 



Reference. Species. 



Pl. II, fig. 2. ' Cosmoceras n. f.* 



3. ' Perisphinctes suhtilis ' 

 Neumayr. 



9. ' Feltoceras chauvini- 

 anum ' A. d'Orbigny. 

 21-23. ' Waldheimia boehmi.' 



24. ' Waldheimia concava.' 



19. ' Waldheimia heneckei.' 



Remarks. 



Miicli like JBaculatoceras of nior- 

 tense date. 



Not P. subtilis. Very like 1\ 

 psetidomartinsii Sieuiiradzki — 

 Frorsisphinctes, I, 8, pl. cc ; 

 garantiana. 



More like Caumontisphinctes, I, 8, 

 pis. clxix & cxcii ; niortense. 



' Has the most remarkable likeness 

 to Waldheimia hrodiei S. Buck- 

 man (in Davidson, Mon. Brit, 

 Jur. Bracli. A pp. to Suppl., 

 Palajont. Soc. 1884, p. 266 & 

 pl. xix, figs. 14-15, wliicli is a 

 species from the Iron_y Bed 

 (hlagdeni zone) of Louse Hill.' ^ 



An anamorph of Waldheimia 

 haasi S. Buckman in Davidson 

 as above, p. 265 & pl. xix, 

 fig. 12 ; hlaqdeni zone of Louse 

 Hill. 



A catamorph of Zeilleria ferrn- 

 ginea S. Huckmau, I, 4, p. 260 

 & pl. xiii, fig. 4; from the Irony 

 Bed {hlagdeni zone) of Louse 

 Hill. 



The stratum in question appears from Parona's description ^ to 

 be homogeneous. It is making a rather large, though not 

 impossible, demand on credulit}'- to believe that this homogeneous 

 deposit was persistent without alteration, through all the great 

 number of hemerae which are contained in Upper Inferior Oolite, 

 Fuller's Earth, Stonesfield Slate, Grreat Oolite, Forest Marble, 

 Cornbrash, Kellaways Rock to basal Oxford Clay. Continental 

 authors, it is true, have failed to realize the great time-interval 

 that exists between post-Bajocian and Callovian — being inclined to 

 look upon them as merely a part of one deposit, because on the 

 Continent so many of the stratal constituents are lacking. 

 Quenstedt, for instance, placed such strata just in one division, 

 Braun Jura e, as if they all made up quite a minor episode. But 

 I shall have more to say on that point in a sequel to this paper. 



What concerns us now is the difficulty of thinking that the 

 homogeneous deposit lasted persistently through all this time. 

 There is perhaps no evidence against it in the shape of different 

 deposits in the neighbourhood ; but the great non-sequence 

 suggests that a change of conditions occurred, that different 

 deposits were laid down and were entirely swept away again — 

 then that there was stratal repetition and coalescence. 



The interesting point about the Bui-ton White Bed and the 

 Watton Bed is the definite evidence given for about 230 feet of 

 strata, different from them and differing among themselves- — 

 sands and vaiious limestones — separating two like deposits. Bvit 

 it is not difficult to picture another condition — a difference of 

 geological and geographical history — sea where now is land, the 



1 I. 5, p. 105. 



2 VIII, p. 3. 



