48 » MR. H. W. MONCKTOIf 01S[ THE 



4. 5[%6Bagshot Beds o/Bagshot Heath. By Hoeace W. Monckton, 



Esq., F.G.S. (Eead December 23, 1891.) 



In the ' Geological Magazine ' for August 1891 Dr. Irving advocates 

 the adoption of a twofold division of the beds of the Bagshot Series 

 of the London Basin, and in the ' Proceedings of the Geologists' 

 Association' for July 1891 Mr. Hudleston (p. 102) suggests a slight 

 alteration in the system of subdivision at present adopted for that 

 series. I must say I am opposed to these changes, and I may at 

 once point out that Dr. Irving himself uses the terms "Middle Beds," 

 " Middle Group," and " Lower and Middle Group " in the paper 

 referred to — very good evidence, I think, of the practical convenience 

 of the threefold division now in use. 



I think that a good deal of the controversy which has arisen in 

 relation to these beds is due to the unfortunate adoption by Dr. 

 Irving of the well-section at Wellington College as the type, instead 

 of the much more satisfactory section at Goldsworthy Hill originally 

 adopted by Prof. Prestwich in 1847.^ I call the well-section at 

 Wellington College unsatisfactory for several reasons, one of which 

 is that two accounts apparently of the same well are given in the 

 ' Memoirs of the Geological Survey,' vol. iv. (1872) p. 425, which 

 differ in material details. If they do both relate to the same well 

 I should prefer the account given by Prof. Eupert Jones to that of 

 the well-sinkers, even though they preserved a series of specimens. 



There is one slight alteration which I think Dr. Irving, Mr. E. 



5. Herries, Lieut. Lyons, and myself are all agreed should be made 

 in the classification in Prof. Prestwich's section at Goldsworthy 

 Hill, viz., the top of the hill should be included in the Middle 

 Bagshot — for remains of the Upper Bagshot basement pebble-bed 

 occur on Hook Heath close by.^ With this amendment we have 

 three very well-defined divisions of the Bagshot Beds : — 



1. Upper Bagshot. — Entirely sand, with a pebble-bed at the base ; marine 

 shells of Lower Barton age abundant in places ; 228 feet or more thick at 

 Chobham Eidges. 



2. Middle Bagshot. — Clays, and yellow and green sands with pebbles and 

 marine shells of Bracklesham age (locally abundant) ; about 50 feet thick 

 at Goldsworthy. 



3. Lower Bagshot. — Yellow sands with irregular argillaceous beds ; no fossils 

 except plants yet satisfactorily recorded in the area south of the Thames ; 

 130 feet thick at Groldswurthy, but of very variable thickness elsewhere. 



The greater part of the controversy relating to the Bagshot Beds 

 xefers to the dividing line between the Middle and Lower Bagshot, 

 and this perhaps is mainli/ due to the adoption of a well-section 

 as a type where the junction line cannot be studied, in preference 

 to Goldsworthy Hill, where it can. It is shown at that place in a 



^ Quart. Journ. Geol. Soc. vol. iii. p. 382, fig. 3. 



^ See Lyons, Quart. Journ. Geol. Soc. vol. xlv. (1889) pi. xxi. ; Monckton and 

 Herries, Proc. Geol. Assoc, v^ol. xi. (1889) p. 16. 



