Siliceous Bodies of the Chalk, Greetisand, and Oolites. 221 



fleet the mass of the spongeous portion exhibited nunaerous cylin- 

 drical contorted canals, which from their uniformity and minuteness 

 of diameter, Mr. Bowerbanli considered to be the incurrent canals of 

 the sponge ; and other orifices of greater diameter, to be the excur- 

 rent. Very frequently, when little of the reticulated substance of the 

 sponge remains, its former jiresence, the author says, is indicated by the 

 siliceous matter resembling a congeries of gelatinous globules, mould- 

 ed by the tissue amid which it was deposited ; and the globules, when 

 traced to the edges of the patches of spongeous texture, were found 

 to agree in size and form with the orifices of the supposed incurrent 

 canals. In cases where no traces of the sponge can be detected, Mr. 

 Bowerbank thinks, that the mode in which the spicula, Foraminifera 

 and other extraneous matters are dispersed equally in all parts, and 

 not precipitated to one portion of the flint, indicates that the organ- 

 ized tissue in which they were entangled, retained its form and tex- 

 ture sufficiently long to allow of the fossilization of these remains in 

 their original places ; and that the nature and position of these bodies 

 strongly indicates the former spongeous nature of the flint. 



When the chalk is carefully washed from tiie exterior of a flint, 

 and a portion examined as an opake object with a power of about 

 fifty linear, it exhibits a peculiar saccharine appearance, with deep 

 circular excavations, having fragments of extraneous matters partly 

 imbedded or adhering to them. If the surface be further cleansed by 

 immersion in diluted muriatic acid, till efl'ervescence ceases, spicula 

 may be detected on the sides of the deep circular cavities ; and if, 

 again, a piece a quarter of an inch in diameter, presenting the rough- 

 est aspect, be examined under a power of 120 linear, illuminated by a 

 Lieberkuhn, the surface, under favourable circumstances, will pre- 

 sent a complex mass of small, contorted tubuli, occasionally fur- 

 nished at the apex witli a minute jjerforation. 



The structure and otiier characters of the tabular flints are stated 

 to accord perfectly with those of the nodular masses, except that the 

 under surface has a stifl more marked spongeous aspect, and that spi- 

 cula and Foraminifera are more abundant. The absence of any ap- 

 parent base or point of attachment in the great mass of nodular chalk 

 flints, the author says (considering them undoubtedly of spongeous 

 origin), may be accounted for by supposing that the gemmule was 

 originally attached to some minute fragment of a shell or other sub- 

 stance, and that its further development took place while recumbent 

 on the mud or silt. 



The perpendicular and oblique veins of flint between Brighton 

 and Rottingdean, are reported to present exactly the same internal 

 characters as the tabular and nodular flints, and to agree externafly 

 with the former. The occasional existence of a fissure filled with 

 chalk, in tlie centre of tlie vertical layers, Mr. Bowerbank conceives, 

 may indicate tliat tlie sponge had grown from the two sides of the 

 crevices, but had not in all places been able to unite. The sides of 

 these flint veins are not studded with Foraniinifera in a manner simi- 

 lar to that of the tabular iiorizontal layers. 



Mr. Bowerbank next examined the flint with which Echinites and 



