392 Mr. W. J. Sollas on the Flint 



the deciduous globates of recent Geodia, and in globates which 

 have been treated with caustic potash*. Though Carter was 

 the first to announce the discovery of fossil globates, they had 

 been previously described by Blakef, who, however, regarded 

 them as Foraminifera, owing to those he examined having 

 undergone complete calcification. These interesting pseudo- 

 morphs, which occur in the Coralline Oolite, were named by 

 Blake Renulina Sorbyana. Mr. Hudleston, who, with Blake, 

 is our great English authority on the Coral-rag, was kind 

 enough to place in my hands a thin slice of the North-Grim- 

 stone rag, and some siliceous matter which had been left 

 behind on dissolving a fragment of that rock. In the latter, 

 remains of trifid spicules and globates were readily seen ; 

 in the former, characteristic sections of Renulina, agreeing in 

 form and size with the siliceous globates of the insoluble resi- 

 due, were as clearly evident. A good illustration of these 

 sections as seen in a slice of Grimston rag, magnified 100 

 diameters, is given by Sorby %. Most of the globates of Renu- 

 lina, or, as we may now say, Geodites Sorbyanus, have been 

 completely transformed into calcite ; others have undergone 

 secondary silicification. The amount of silica set free during 

 their transformation into calcite must have been very great, 

 as will appear from the following statement by Sorby § ; he 

 says : — " The Perna bed in Dorsetshire, and also certain beds 

 in Yorkshire, are remarkably rich in the small reniform shells 

 named by Mr. Blake Renulina, which constitute as large a 

 part of the bulk of the rock as the Foraminifera do in all 

 but a very few exceptional specimens of chalk." 



Hudleston || has since clearly recognized the nature of 

 Renulina ; but Blakef appears to dispute it. 



Rhopaloconus tuberculatus. (PI. XX. fig. 46.) 



This spicule has the form of a cone with rounded ends ; its 

 surface is covered all over by regularly disposed tent-like 

 tubercles. It varies in length from j^ to ^ inch. 



Pachcena Hindi. (PL XX. figs. 44, 52, 56, 64, and 69.) 



There is a similarity of facies about these large thick 

 spicules which leads one to group them together ; we have 



* Sollas, " Action of Caustic Potash," Annals, ser. 4, vol. xx. pi. ix. 

 figs. 8-11. 



t Blake, ' Monthly Microscopical Journal,' 1876, vol. xv. p. 262. 



X Presidential Address, London Geol. Soc. vol. xxxv. pi. vi. fig-. 1, 

 p. 70 (sep. copy). § Loc. cit. p. 51. 



|| Proc. Geol. Assoc, vol. v. p. 443. 



f Ibid. p. 266. 



