312 Dr. H. B. Eoll—On Fossil Spoiiges. 



based on the supposition that they would not otherwise have escaped 

 compression, and partly on the circumstance that Polyzoa, Serpulce. 

 Ostreidce, etc., frequently found attached parasitically to the surface 

 of the sponge have been observed to exhibit the worn appearance 

 produced by the rolling of hard bodies on the sea-bed. Moreover, 

 they say that compressed specimens show more or less distinctly the 

 signs of fracture. But while this may be true of some of those 

 sponges that had a solid siliceous framework, it certainly is not gene- 

 rally the case, and examples of Hippalimus, Ischadites, Mortieria, and 

 many other sponges more or less distorted by compression, are suffi- 

 ciently abundant. That they should not — especially the cup-shaped 

 sponges — be more often compressed than they are may, perhaps, be 

 a matter of surprise. But this is probably due to the circumstance 

 that the fine muddy sediment in which they were entombed had so 

 insinuated itself into the interspaces of the sponge as to afford an 

 equal amount of support on all sides.^ Moreover, some further 

 explanation will suggest itself when speaking of the sponges of 

 Farringdon, and the manner in which fossilization of the sponge 

 appears to have often taken place. 



Whether Polyzoa and other parasites are really more frequent on 

 the fossil than on the recent sponge is a question I am not prepared 

 to answer. But M. De Fromentel is certainly not correct in say- 

 ing that they never occur upon recent sponges ; and very frequently 

 the adhesion of the parasite to the fossil sponge is more apparent 

 than real, being produced solely by the cementing influence of 

 fossilization, and by the nature of the matrix in which they are 

 embedded. In any case, unless the Polyzoa grew upon dead indi- 

 viduals, the nature of the skeleton could have had no influence upon 

 the parasite, as, whatever it may have been, it was equally invested 

 by the sarcode of the animal. That the Serpulae and Ostreida3 some- 

 times became attached to the sponge while living is apparent from 

 their having become partially embedded in the sponge tissue which 

 has grown over them ; but it is so also with recent sponges : and as 

 regards the worn appearance of the parasites and other foreign 

 bodies occasionally found attached to the sponge, it is quite possible 

 that they may have undergone attrition before they became adherent ; 

 and, moreover, the fossil itself may have been derived from pre- 

 existing deposits, as were the Oolitic forms found in the gravels 

 of Farringdon. 



But there is, in fact, no real ground for assuming with D'Orbigny 

 and others, that the skeleton of the fossil sponges was necessarily 



1 The compression often observed in fossils, especially those of the older rocks, is 

 probably due to the squeezing to which they have been subjected in the charge of 

 position and contortion of the beds in which they occur, rather than to the dead 

 weight of the superimposed sediment. It is now well known that Starfish and other 

 soft animals, even at the great depths of mid-ocean, are not compressed, owing to the 

 pressure being applied equally on" all parts. Prof. Sars dredged sponges, actinozoa, 

 true molluscs and worms at a depth of 300 fathoms; and the Swedish deep-sea 

 dredgings, in the expedition to Spitzbergen, brought up Crustacea, moUusca, and 

 annelids, at depths of from 6000 to 8400 feet. Quoted in Intellectual Observer for 

 December, 1866, p. 400, from Annals of Nat. History. 



