252 Mr. J. S. Bovverbank on the Siliceous Bodies of the Chalk. 



istence of an elective attraction between tbe siliceous matter and 

 animal and vegetable remains ; nor offer the slightest explanation 

 of the cause of the suspension in all parts alike of the masses of 

 siliceous spicula, the remains of polythalamous shells, small 

 branched corals and numerous other animal bodies ; nor account 

 for the continually recurring presence of that tissue, which I have 

 described as, and still believe to be, portions of the skeleton of 

 the sponge to which the great mass of chalk flints owe their ori- 

 gin. If this description of tissue were found only in the flints of 

 the chalk, there might remain room for doubt of its being that 

 which I have asserted it to be ; but when we find that the flints of 

 the Portland oolite afford similar remains of a corresponding tis- 

 sue, but specifically different from that of the chalk flints, and 

 that circumstances of the same description obtain in the flints of 

 the greensand formation and in those of the mountain limestone, 

 such doubts cease to exist, and the fair philosophical inference is, 

 that those tissues are in truth the remains of the spongeous 

 bodies to which these siliceous masses have been indebted for 

 their form. 



The author then proceeds to ask*, " Where, in recent sponges, 

 do we find the innumerable quantities of shells and other large 

 objects that we find in the chalk flints ?" And after describing 

 some flints with numerous shells attached to them, and spe- 

 cimens of which kind are by no means rare, he proceeds thusf : 

 *' I have seen, in Mr. Eowerbank's valuable collection of sponges, 

 a specimen in which one small shell is imbedded : this may have 

 happened in casual instances with small dead shells, but where 

 can it be found, in recent sponges, from the most favourable spots, 

 that they are full, as we find the flints full, of bivalves large, nu- 

 merous and perfect, and apparently living when enveloped ?'' In 

 the paragraph immediately preceding the one last quoted, Mr. 

 Smith describes his specimens of flint, not as being full, but 

 merely as having shells attached to the surface of the flint, for he 

 says of the shells in the conclusion to the description of the flints 

 alluded to : "These are lying on the external surface, just sunk, 

 as it were, in the flint, as they would sink in water, but not at all 

 covered.^' But the author does not give us the slightest expla- 

 nation of the extraordinary phsenomenon he describes of shells 

 partially sunk into all parts of the surface of an irregularly 

 formed nodule of water or fluid silex " of most fantastic form,''^ 

 to quote his own words. It would appear most natural to sup- 

 pose that the mode of their sinking in water would be at once to 

 the bottom, and not merely to indent the surface and there re- 

 main, while, on the contrary, their position is quite natural if the 



* Page 4. f Page 5. 



