A. J. Jukes-Browne — Zones of Lower Chalk. 507 



8. SUMMAKY. 



In conclusion, the main results of our researches in the Lower 

 Carboniferous rocks of North Wales may be epitomised as follows : — 



1. The classification of these rocks here given is absolutely based 

 on palseontological data : it has been shown that all the errors in 

 previous work can be traced to the subordination of palaeontology 

 to the lithological features of the strata. 



2. The sequence exhibited in the area under examination is 

 perfectly normal to that obtaining in other areas of the North 

 Midlands, which afforded the key to the simple explanation of the 

 succession in this district. For the purposes of correlation the 

 perfection of Ihe geological record has exceeded our most sanguine 

 expectations. 



3. The Holywell shales have been proved to be the equivalents, 

 lithologically and palseontologically, of the Pendleside Series. 



4. The lower series of the Carboniferous Limestone as developed 

 in the Bristol area was never deposited in these parts, whose lowest 

 beds are characteristic of a comparatively late phase of the Car- 

 boniferous Limestone period. Whether this was altogether due to 

 irregular configuration of the ocean floor of that age, or to con- 

 temporaneous earth-movement of a specially regional character, it is 

 much too soon as yet to argue with assurance. 



Our thanks are largely due to Dr. A. Vaughan, who has kindly 

 looked over a large number of Corals and Brachiopods and compared 

 them with the forms occurring in the upper portion of the Bristol 

 Carboniferous area. We also have to thank Dr. A. Smith Woodward 

 and Mr, R. Kidston for the determination of some fossil fish- and 

 plant-remains. 



IV. — The Zones of the Lower Chalk. 

 By A. J. Jukes-Browne, B.A., F.G.S. 



IN the September number of this Magazine Mr. T. 0. Bosworth 

 raises some questions with regard to the zoning of the Lower 

 Chalk in general, and of Cambridgeshire in particular. As I am 

 responsible for the subdivision of the Lower Chalk of this country 

 into zones I suppose the matter concerns me more than anyone else. 



The two main questions raised by Mi'. Bosworth are (1) the zonal 

 position of the Totternhoe Stone, (2) the propriety of using Holaster 

 subglobosus as an index for the higher zone. He may be sure that 

 both these points were fully considered by me when compiling the 

 account of the Lower Chalk for the Geological Survey Memoir on 

 Cretaceous Rocks, and he is probably aware that the second point 

 was discussed in the second volume of that Memoir (chapter ii, p. 17). 



With respect to the Totternhoe Stone, Mr. Bosworth should explain 

 why he uses the term " Burwell Rock "; this name may be current 

 at Cambridge, but it cannot supplant the older name of Totternhoe 

 Stone, and his own diagrams show tliat he accepts the identity of 

 the stone beds at Totternhoe and Burwell. 



