554 ON SOME FOSSIL SPONGES FROM THE INFERIOR OOLITE. 



Dr. Hlnde expressed his regret that Prof. Sollas was not present to 

 read his own paper, and especially that it was accompanied by neither 

 diagrams nor specimens. Mr. Whidborne was to be congratulated on 

 the discovery of Sponges in a formation where hitherto they had not 

 been noticed, and even on the same horizon on the continent they 

 were not common. The speaker had not found a single siliceous 

 Sponge from the Jurassic strata of this country in the Jermyn-Street 

 or British-Museum collections, though on the continent siliceous 

 Sponges were common, especially in the "White Jura. The replace- 

 ment of the siliceous skeleton by calcite was a fact well known to 

 students. A specimen placed in acid would be in part wholly dis- 

 solved, while another part would stand out quite clear and perfect. 

 The change certainly had taken place ; but the chemistry of it was 

 not yet fully understood. However, there was no doubt that the 

 " organic" silica in sponges was in a very unstable condition. In 

 the Upper Chalk of this country, for instance, only the casts remained. 

 As regards the Pharetrones, which Prof. Sollas regards as incertce 

 seclis. they were regarded by Zittel as allied to calcareous Sponges 

 now existing in shallow seas. This view had been combated by 

 Mr. H. J. Carter and Prof. Sollas. Dr. Steinmann had also con- 

 sidered them not to be calcareous Sponges but allied to Hydrozoa. 

 He (Dr. Hinde) had examined Pharetrones in the British Museum, 

 and discovered in some of them spicules so exactly like those of 

 existing Calcispongiae, in their form and position, that their alliance 

 with living forms could hardly be disputed. The accuracy of this 

 had now been admitted by Mr. Carter ; and Dr. Steinmann had with- 

 drawn his former views respecting them. He did not consider that 

 the occurrence of Hexactinellids with these sponges would vitiate 

 the general evidence for the deep-water habitat of Hexactinellid 

 sponges. 



Prof. Hughes said that further information was wanted as to the 

 circumstances under which this replacement of silica by calcite took 

 place. He asked whether it might have occurred at such a depth 

 as would keep the water, while it was saturated with carbonate of 

 lime and was under great pressure, also at a sufficiently high tem- 

 perature to carry away the silica in solution. In support of this 

 suggestion he pointed out that where flint is common in the Upper 

 Chalk, there is generally evidence that it was formed after the chalk 

 had been raised and exposed to surface-action such as allows of 

 shrinkage and opening of joints. This is especially shown by the 

 tabular flint along joints oblique to the bedding. 



Dr. Woodward called attention to some specimens in the British 

 Museum which would be interesting to Professor Hughes, and 

 made some observations on the formation of flint. 



The Bev. G. P. Whiddorke said that he was acquainted with the 

 labours of Mr. Moore mentioned by Mr. Win wood. ' Prof. Sollas had 

 intended to be present, and would have brought specimens, but was 

 prevented at the last moment from coming. 



