520 MK. S. S. IJUCKMAX ON THE SO-CALLED 



from the section at Jiiirton-Eradstock * : and, although somewhat 

 outside the scoije of this paper, it may be interesting to call atten- 

 tion to it. This is in regard to the bed with Ludiuvjia MiircJtisonce, 

 from which I collected several fine specimens ; but at Burton-Brad- 

 stock I neither detected this species, nor a bed of similar matrix. 



At the neighbouring Symondsbury Hill I found Lxuhuigia Mur- 

 cliisonce and Lioceras opalinum in the same bed ; and this bed was 

 probably on the horizon of " 5," " part unseen," at Chideock Hill. 

 The occurrence of these two species together is a most interesting 

 fact, rendering it rather difficult to draw any line of demarcation 

 between the Lias and the Oolite at the top of the Opalinmn-zoiLic. 



Not only do the lowest beds of the so-called " Inferior-Oolite 

 Limestone " belong to the Opalimtm-zone, but the upper portion of 

 the Yeovil Sands as well, a fact which the Burton-Bradstock section 

 showed very noticeably, (In this case also we have parts of the 

 same horizon receiving two distinct names.) Purther down in the 

 Sands there is good evidejice, at Burton-Bradstock, of the Moorei- 

 beds (lower part of the Opalimim-zoue) with Grammoceras aalense, 

 &c. Where the 3Ioorei-heds begin and the Dumortieria-heds 

 (upper part of Jure nse- zone) end cannot, as in the Cotteswolds, be 

 stated with certainty : but at the base of the Sands of Down Cliffs, 

 and also in the yellow Sands of Ham Hill, we have species of Du- 

 mortieria, showing clearly that the lower part of the Yeovil Sands 

 belongs to that horizon. This, again, is borne out by the section at 

 White Lackington, where the argillaceous deposits immediately 

 hehiu the Sands show the fauna of the Bisjjansum-'beds, that is, of 

 the beds next in descending order in the Cotteswolds. 



The Blue Clay of Down Cliffs, however, does not contain, so far 

 as I could discover, any trace of the Dis20(insum-heds. It yielded 

 only Ammonites of the Dumorticria-horizon. It is, therefore, of 

 rather later date than the Clay of the White-Lackington section ; 

 and still more, therefore, is it of much later date than what is 

 generally known as l^pper-Lias Clay, — namely, the Commune- and 

 Falciferu7n- zones. At Down Cliffs the only representative of the 

 Commune- and FaJcife rum-zones i& to be found in the Pink Lime- 

 stone, which lies at the base of the blue shale f. It is 10 inches 

 thick, and really contains two layers. Extended search, judging 

 from other localities which have been carefully and mhiutely 

 worked, would reveal a distinct fauna for each of the beds. 



The foregoing remarks furnish additional evidence of the unre- 

 liability of a grouping which depends on lithologinal appearances. 

 This was one of the points of my former paper ; and it was because 

 no satisfactory line could be drawn between the Lias and the Oolite, 

 as is usually proposed, that I supported the Continental plan of a 

 grouping upon pakcontological grounds, which would combine the 

 Upper Lias and the lower pait of the Inferior Oolite under the term 

 " Toarcian." The following statements in support of this view may 



* Op. cif. p, 45 L 

 t Op. cif. p. 458. 



