306 Dr. E. Hull. Note on Dr. Hindis Paper [Apr. 28, 



vestigation by my colleague, Mr. Hardman, and myself,* and corrobo- 

 rated by the independent investigations of M. Renard in Belgium ;f 

 and I wish to show how improbable it is that siliceous sponges could, 

 by their dissolution, have taken any important part in the formation 

 of the chert-beds of the Carboniferous Limestone either of Ireland or 

 Belgium, or as far as I am aware of any other country. My argument 

 will be based on the fact that the development of sponge-life in the 

 seas of the Carboniferous period was insignificant, and quite inade- 

 quate to account for the existence of bands and masses of chert, 

 sometimes constituting almost a half or a third of the entire mass of 

 the Upper Limestone. J 



Let us now enquire what are the relative proportions of the genera 

 and species of siliceous sponge-structures to those of calcareous forms 

 both in Carboniferous and Cretaceous strata — assuming that the genera 

 and species indicate to some extent the numerical development of 

 these respective forms. In this comparison I shall omit from con- 

 sideration the mollusca and molluscoidea — though in themselves very 

 important, and altogether lime-forming organisms. In drawing up the 

 following table (p. 307) I have availed myself of the lists published 

 recently by Mr. Etheridge, F.R.S., which make the comparison simple 

 and easy.§ 



The contrast of the non-molluscan fauna of the two periods will be 

 at once apparent (1) in the enormous proportion of siliceous sponges 

 in the Cretaceous as compared with those of the Carboniferous periods ; 

 and (2) in the predominance of corals and crinoids in the Carbonife- 

 rous period. The insignificant representation of siliceous sponge- 

 structures in the Carboniferous seas as compared with the calcareous 

 foraminifers, corals, and crinoids will also be apparent. As compared 

 with the development of these forms in the Carboniferous period, it 

 will be seen that the species of siliceons sponges might almost be 

 counted on the fingers of the two hands ; both in genera, species, and 

 individuals they are quite unimportant as compared with the calca- 

 reous organisms of that period, and totally inadequate to supply mate- 

 rial for the formation of such beds of chert as are formed in the 

 Carboniferous Limestone formation. The enormous predominance of 

 the calcareous organisms in this formation is a fact which cannot be 



* " On the Nature and Origin of Beds of Chert of the Upper Carboniferous 

 Limestone of Ireland." 'Scientific Transactions of the Royal Dublin Society,' 

 vol. 1, 1878. 



t " Recherches lithologiques sur les phthanites du calcaire carbonifere de 

 Belgique." Par M. A. Eenard. 'Bulletin de l'Aeademie Royale de Belgique,' 

 vol. 46, 1878. 



X As in the case of the Upper Limestone of Florence Court, near Enniskillen, 

 altogether 400 feet thick, of which perhaps 150 are formed of chert-bands, inter- 

 calated with those of limestone. 



§ Phillips' 1 Manual of Geology,' Edit. 1885, Part II. 



