279 



THE ZONES OF THE LOWER CHALK. 



The combined excursion into Lincolnshire of the Geologists' Association 

 and the Yorkshire Geological Society, which took place five years ago, has 

 had at least one very beneficial result ; for, quite apart from the value of 

 any work which may have been done on that particular occasion, it has 

 fortunately been the means of arousing among the residents of that part 

 of the country, an interest in the many fascinating problems bearing upon 

 the geology of their own county. 



One evidence of this newly awakened interest is the paper on the Lower 

 Chalk of Lincolnshire recently published by the Rev. C. R. Bower and Mr. 

 J. R. Farmery.* Being residents in the district, the authors have naturally 

 been able to devote much more time to the collection of fossils than was 

 possible on the part of the officers of the Geological Survey who worked 

 over that area, a,iid taey have therefore been able to make some useful 

 additions to the previous lists. 



It is, however, in my opinion, regrettable that the records of such 

 useful field work should have been mixed up with an attempt to re-arrange 

 the zonal classification of the Chalk, in a manner which practically revolu- 

 tionises the existing system. The authors propose to designate the lowest 

 part of the Chalk up to and including the Totternhoe Stone, the ' Zone of 

 Holaster subglosus.' For the lower pink band above the Totternhoe Stone 

 they create a new sub-zone characterised by Terebratulina ornata. The 

 beds above this, up to the Actinocamax plenits marls, are to be the ' Zone 

 of Holaster trecensis.' This is not suggested as a merely local arrangement, 

 for they say (pp. 337-8) — 



" The zonal nomenclature adopted by the Geological Surv-ey for 

 the Lower Chalk of Lincolnshire seems to us to be unsuitable .... 

 But the link in the chain of evidence supplied by a study of the Lower 

 Chalk of Lincolnshire suggests that the use of the names of these 

 two fossils [Holaster siibglobosus and Holaster trecensis) might be 

 made the basis of a zonal scheme which would apply to the whole of 

 the Chalk area of England.' 

 The effect of this would be as follows : — 



Current. Proposed. 



Zone of Holaster siibglobosus -— Zone of Holaster trecensis. 



Zone of Ammonites varians = Zone of Holaster siibglobosus 



Let us see, then, how this works out. It is true that in Lincolnshire 

 Holaster siibglobosus does range down to the lowest beds of the Lower Chalk. 

 But this is certainly not the case in many other parts of England. For 

 example, in Kent, Holaster snbglobosus does not occur in the zone of Amnio- 

 ■nites varians, but is found associated with Holaster trecensis in the zone 

 above. The .same is the case in Surrey, Berkshire, Oxfordshire, Bucking- 

 hamshire, Bedfordshire, Cambridge, Hertford and Suffolk. In none of 

 these counties has Holaster siibglobosus been recorded below the horizon of 

 the Totternhoe Stone. Neither is it so rare in the higher beds of the Lower 

 Chalk as Messrs. Bower and Farmery seem to suppose, for in Devonshire, 

 the Isle of Wight and in Norfolk, it is found right up to the Actinocamax 

 plenus band. In Yorkshire it is common at this horizon, for Mr. W. Hill 

 says t — 



' Holaster subglobosus occurs throughout the Lower Chalk in the 

 Speeton cliffs. Holaster subglobosus occurs from the base of bed 3 to 

 the Belemnite marls.' 



* ' Proceedings of the Geologists' Association,' Vol. XXI., part 6. 

 ' The Zones of the Lower Chalk of Lincolnshire.' 



t ' Q. J. G. S.', Vol. XLIV. (1888), part 3, pp. 345-35-2. ' The Lower 

 Beds of the Upper Cretaceous Series in Yorkshire and Lincolnshire.' 



1910 July I. 



