200 W. H. Hudleston — Creechharrow in PurbecJc. 



notice belts of clear calcite also in the annular system, especially 

 towards the interior, giving the rings an agate-like appearance. 

 The core, or centre of the pisolite, consists of the matrix partially 

 modified, but without the brown specks which characterize it. This 

 appears to be the case in all sections of the pisolites which I have 

 examined, and suggests that the slight amount of colouring matter, 

 due to iron oxide, which characterizes the rings of brown calcite, 

 has been transferred from the included portion of the matrix to the 

 annular system surrounding it by a sort of centrifugal flow-action, 

 such as that which forms the ironstone shells of limonitic deposits. 

 In the case of some of the pisolites the centre consists of clear 

 crystalline calcite, making the analogy with the ordinary siliceous 

 agate still more complete. 



There remains only one further remark to make in dealing with 

 these curious pisolites, and that refers to a suggestion that these 

 concretionary bodies may possibly in the first instance have been 

 due to Nummulites. Everything tends to refute this supposition, 

 more especially the association of these pisolitic limestones with 

 Paludina and Melanopsis. Yet it must be admitted that there is 

 a considerable resemblance to limestones showing sections of 

 Nummulites, although the resemblance is apparent rather than real, 

 as may be seen on closer investigation, and it can be safely affirmed 

 that nothing approaching organic structure has hitherto been 

 detected in these pisolites. It is certainly a curious coincidence 

 that both Nummulites lavigatus and N. elegans occur in the Lower 

 Eocenes of this country, mainly perhaps in the Brackleshams, but 

 also in the Barton Beds ; so that, if the Creechharrow Limestone had 

 been of marine origin, there would have been nothing surprising 

 in the occurrence of Nummulites in any beds of Bagshot or of 

 approximate age.^ 



Palceontology. — Very little can be said under this head, as the only 

 specimens of fossils from the Limestone have been derived from the 

 limited area of the summit pit or the immediate neighbourhood. 

 There can be no doubt that Paludina is fairly common, as it occurs 

 both in the form of shells and casts by no means infrequently. The 

 shells are often obscured by a concretionary investment, as previously 

 stated, but there is sufficient material to form a fair idea of the 

 species. It is a form which clearly difi'ers from the ordinary 

 Purbeck species {P. carinifera and P. elongata), but which has 

 a fairly good resemblance to the Bembridge species, Paludina lenta, 

 Solander.- 



1 According to Professor Eupert Jones, writing of the physical features of the 

 Bagshot district in 1880 (Proc. Gaol. Assoc, vol. vi, p. 437), "the Bagshot sands 

 are the shallow water and western equivalents of the great Nununulitic formation, 

 which is represented in the east by the thick Nummulite limestones, deposited in the 

 open ocean of the period." 



2 In my paper in the Geological Magazine (1902, p. 251), I referred this form 

 to P. media, Woodw., a synonym of P. lenta, Solander, the latter being the correct 

 name. The history of F. lenta is rather a singular one. It was first described by 

 Solander (1766) in Brander's Foss. Hants, and is regarded as ranging from the 

 "Woolwich (and Beading) Beds to the Hempstead, Bembridge, and Headon Beds. 

 Hence it is essentially an Eocene and Oligocene species. 



