PROCEliDINGS Ol" THE COTTESWOLD CLUB 211 



numerous and varied in shape. The si)ongcs of the 

 chalk are very numerous ; some authorities, in fact, con- 

 sider that the flints are formed solely from the silex 

 derived from silicious sponges by a process of dissolution 

 and re-solidification. Other authorities hold difl'erent 

 views ; but, as I do not propose to enter upon a dis- 

 cussion as to the origin of flints, sufllice it to say that 

 a very considerable percentage of flints contain well- 

 preserved sponge spicules, and spicular network, and 

 in some cases entire sponges, enclosed in their masses. 



All the chalk sponges appear to belong to the silicious 

 class — at least I am not aware of any calcareous form having 

 been found — and comprise the orders Tetractinellidse 

 and Hcxactinellidse. To the former belong the spicules 

 which have 4 rays proceeding from a centre, the stellar 

 forms, such as occur in Tethya, and probably all the 

 acicular s})icules. The latter order comprises the Ven- 

 triculites and their allies, which have a continuous spicular 

 skeleton forming a beautiful though complex network. 

 The structure of the spicular network of the Hexactinellids 

 is best seen in sections of flint, although in the majority 

 of specimens the finer structure is so completely obscured 

 by iron oxide that the elegant lantern nodes at the points 

 of intersection cannot be made out. 



In some localities the chalk contains great numbers of 

 ostracoda belonging to the genera Cytherella, Cythere, 

 Cytliereis and Bairdia. In a small piece of chalk taken 

 from the hollow of a flint at Caterham Junction, I 

 found no fewer than 5 different species, comprising all 

 the above-named genera, except Cytherella. 



Coccoliths, as I have stated above, occur in chalk in 

 immense numbers : I have never yet examined a piece 

 without finding them. These bodies are exceedingly 

 minute, and require a magnification of 800 to 1000 

 diameters. Even then, to see them at all satisfactorily, it 



