54)6 Geological Society, 



fibres, but which exhibited numerous long and simple thread-like 

 fibres apparently much decomposed, as their substance consisted 

 sometimes of a congeries of minute separate particles, and sometimes 

 of straight or curved lines composed of minute black bodies. In 

 other cases these strings of incipient gemmules were contained 

 within the boundaries of the tubes, and then presented rarely more 

 than a row of single gemmules ; but occasionally the diameter of the 

 vessels appeared to have been much enlarged, and the gemmules 

 were indiscriminately dispersed within its cavity. In some instances 

 also they exceeded in diameter the vessel or its remains, as if they 

 had outgrown and burst their natural boundary, or the walls of the 

 latter had contracted. From the close resemblance in the structure 

 and contents of these vessels to those contained in the large sponge- 

 fibre first described, Mr. Bowerbank has little doubt, whatever may 

 have been their original nature, that they are the same kind of tissue, 

 under somewhat different conditions. 



In all the agates and jaspers which have been microscopically in- 

 vestigated by the author, the spaces not occupied by remains of 

 spongeous texture were filled with silex or chalcedony arranged in 

 bands which conformed more or less to the outline of the enclosed 

 fossil. Where, however, the matrix consisted of radiating crystals, 

 the decayed animal remains frequently appeared to have been impelled 

 forward, in the same manner as the decomposed cellular portions of 

 fossil wood have often yielded to the crystallizing process of the as- 

 sociated mineral matter. 



Egyptian jaspers, Mocha stones, fyc. — The author has examined 

 also numerous specimens of polished Egyptian jaspers, which, when 

 viewed as opake objects, by direct light and with a power of 150 

 linear, were found to consist of finely comminuted light buff or brown 

 irregular granules, cemented by semi-transparent silex, very much 

 resembling the state in which it exists in chalk-flints and greensand 

 cherts, and to the variations in its colouring matter the banded ap- 

 pearance of the jaspers is due. Imbedded, but very unequally in 

 the layers composing the jaspers, Mr. Bowerbank discovered hun- 

 dreds of beautiful foraminifera closely resembling those found in 

 chalk-flints, and often difficult to distinguish from the species found 

 in the Grignon sand of the calcaire grossier. 



The Mocha stones which the author has examined, presented no 

 indications of organic structure, the moss-like delineations and other 

 appearances, resembling beautiful, thin, reticulated tissues, being due 

 to dendritical or metallic infiltrations. * 



In the larger pebbles of a mass of Herefordshire pudding-stone, 

 Mr. Bowerbank discovered the characteristic spongeous structure of 

 chalk-flints. 



In conclusion, the author dwells upon the difficulties attending 

 the study of the bodies which he has examined and described, in 

 consequence of the little attention which has been paid, with few 

 exceptions, to the structure of recent sponges ; and he states that 

 the aspect of the latter, when viewed by the unassisted eye, is so 

 different from that which it presents when seen under a high micro- 



