308 



Mr. E. T. Hardman. 



[Apr. 28, 



who considers that M. Renard has mistaken sponge-spicnles for 

 crinoid stems.* 



In conclusion, it maybe asked what is the evidence which Dr. Hinde 

 can assign for his statement — that the silica of Carboniferous chert 

 has been derived from sponge-spicules ? Absolutely none, except a 

 fanciful analogy between these peculiar masses and the sponge-beds 

 of the Cretaceous formation. On the other hand, it has been shown 

 that no such analogy exists, inasmuch as there was a marked contrast 

 between the organic beings in the waters of the Carboniferous seas as 

 compared with those of the Cretaceous period. In the former siliceous 

 sponges were exceedingly rare ; in the latter they abounded ; so that, 

 whatever part they may have played in the construction of the Creta- 

 ceous bands of chert, it is clear they could have taken no important 

 part in the formation of the chert-bands of the Carboniferous Lime- 

 stone. The relative weight of opinion as expressed in the papers 

 dealing specially with this subject must be left to individual judgment ; 

 in forming this judgment, however, it will not be overlooked that 

 identical conclusions have been arrived at regarding the mode of 

 formation of the Carboniferous chert-bands by two sets of observers 

 working independently, one in Ireland the other in Belgium, almost 

 at the same period, and both using chemical and microscopical 

 appliances. 



I trust, therefore, that I have succeeded in showing that there are 

 good grounds for the opinion of those who consider that the beds 

 and nodules of siliceous material in the Carboniferous Limestone have 

 been formed by a direct replacement of original calcareous matter of 

 the limestone itself by silica held in solution in the ocean-waters, and 

 that, consequently, Dr. Hinde is not justified in referring them for 

 their origin to sponge-structures. 



II. " Note on Professor Hull's Paper." By Edward T. Hardman, 

 of the Geological Survey of Ireland. Communicated by 

 E. Hull, F.R.S. Received April 5, 1887. 



Dr. Alleyne Nicholson, a palaeontologist of no small repute, refers 

 to this subject in his work on the ' Ancient Life History of the 

 Earth,' p. 34. He considers that the silica which has surrounded and 

 infiltrated the fossils which flint contains, must have been deposited 

 " from sea- water in a gelatinous condition, and subsequently have 



* Dr. Hinde's words are : " There are shown, however, in one of the figures 

 (fig. 2) accompanying M. Renard' s paper, circular sections which more nearly 

 resemble those of sponge-spicules than of crinoid stems, to which they are assigned." 

 Note, loc. cit., p. 433, 



