460 Geological Society, 



to the action of the weather, or water, or to original irregularities in 

 the composition of the stone. 



A paper " On Moss Agates and other Siliceous Bodies," by John 

 Scott Bowerbank, Esq., F.G.S., was then read. 



In a paper " On the Origin and Structure of Chalk-flints and 

 Greensand Cherts*," Mr. Bowerbank inferred that the sponges from 

 which he conceives those bodies originated, differed from recent kera- 

 tose sponges only in having possessed numerous siliceous spicula. 

 Since that paper was read, the author, however, has found in true 

 keratose sponges from Australia f, as well as in the sponges of com- 

 merce from the Mediterranean and the West Indies]:, siliceous spicula 

 in great abundance. All discrepancies, therefore, between the extinct 

 and modern types of a portion of the animals under consideration, he 

 says, is now removed. In these prefatory remarks, Mr. Bowerbank 

 likewise states that there is at present only one known species of 

 recent sponge (S. jistularis) the fibre of which is truly tubular. 



The author then proceeds to detail the evidences of the existence 

 in moss agates from Oberstein and other parts of Germany, as well 

 as from Sicily, and in green jaspers from India, of the remains of 

 sponges, in the following order : 1st, the proofs of the fibrous struc- 

 ture ; 2nd, of the preservation of gemmules ; and 3rd, those of the 

 existence of vascular structure. The specimens were examined as 

 opake objects, with direct light concentrated by a convex lens. 

 The number of agates amounted to nearly 200, and that of green 

 jaspers to about 70. 



1. Fibrous structure. — Though polished agates afforded Mr. Bow- 

 erbank, in almost every specimen, strong evidence of spongeous origin, 

 yet the structure and arrangement of the fibres were seldom per- 

 fectly preserved throughout, presenting every intermediate state from 

 complete decomposition to the most distinct spongeous tissue. The 

 siliceous matrix of these remains exhibited a clear and frequently 

 crystalline aspect, but the prevailing tint of the enclosed organic 

 matter was bright red, brown, or ochreous yellow ; occasionally, how- 

 ever, the fibre was milk-white or bright green. The colouring mat- 

 ter was generally confined within the bounds of the animal tissue, 

 leaving its surface smooth and uninterrupted; sometimes it occurred 

 only in the interior of the tubular fibre, the sides being semipellucid 

 or milk-white ; whilst in other cases not only the fibre was com- 

 pletely charged with colouring matter, but the surface was also 

 slightly encrusted with it. In an agate believed to be from Sicily, 

 the greater part consisted of a confused mass composed of innume- 

 rable bright red fibres with no perceptible remains of surrounding 

 structure, but near the margin of the specimen the tubuli were as 

 perfectly preserved as in a recent sponge, presenting a semi-pel- 

 lucid and horny-looking substance enveloping red fibres. In those 

 instances in which the red pigment did not appear to have entered 



* See Geol. Trans., 2nd Series, vol. vi. Part 1. 1841. Proceedings, 

 vol. iii. p. 278, 1840. 



t Annals of Nat. Hist., April 1841. 



X Microscopic Journal, vol. i. No. 1, p. 8, 1841. 



4r 



