1887.] 



on Sponge-remains in the Greensand. 



307 



Table showing the Genera and Species of Invertebrata, other than 

 Mollusca, in the Carboniferous and Cretaceous Periods. 



Protozoa / Siliceous sponges 

 (.Calcareous 



Echinodermata { cAnoids^. 



Total -1 Siliceous sponges 



\ Calcareous organisms 



Carboniferous. 



Cretaceous. 



Observations. 



Grenera. 



Species. 



G-enera. 



Species. 



6 



2 

 15 



2 

 39 



9 

 18 

 11 

 28 



12 



2 

 43 

 3 



144 



30 

 109 



34 

 13V* 



74 

 13 



39 

 ? 



37 

 43 

 5 

 4 

 40 

 59 



162 

 50 



171 

 ? 



76 

 188 

 13 

 14 

 110 

 114 



There is a slight 

 uncertainty re- 

 garding the nu- 

 merical propor- 

 tion of the sili- 

 ceous and calca- 

 reous sponges of 

 the Carboniferous 

 period. 



6 

 121 



12 



514 



74 

 240 



162 

 736 



Chiefly Entomostraea of the Upper Carboniferous stage. 



disputed by those who have had opportunities of studying its charac- 

 ters, either in the north of England, in Ireland, or in Belgium, where 

 whole beds may be observed composed almost entirely of crinoid stems 

 and corals ; while the microscope generally reveals other calcareous 

 forms, such as those of foraminifera, which are invisible to the naked 

 eye, or under the lens. If, then, these original calcareous structures 

 have become silicified, whence could the silica have been derived if not 

 from the circumambient waters of the ocean under certain special and 

 favourable conditions of temperature ? 



In his paper on the origin of the beds and nodules of chert (phtha- 

 nite) in the Carboniferous limestone of Belgium, M. Renard expressly 

 identifies crinoid structures, not only in circular disks of the cross- 

 section of the stems or ossicles, but in the more solid and structure- 

 less masses of the chert when treated with acid ;* and he expressly 

 states that the silicification has supervened in the case of an originally 

 calcareous rock-compound chiefly of foraminifera, crinoids, and corals ;f 

 and, as Dr. Hinde himself admits, M. Renard distinctly states that 

 there is no evidence that the infiltered si lex into the limestone is 

 derived from the decomposition of sponge-spicules or frustules of 

 diatoms. Surely such a statement from so competent an observer is 

 entitled to more consideration than that accorded to it by Dr. Hinde, 



* Loc. cit., p. 492. 

 f I hid., p. 196, 



