324 
MISCELLANEA. 
FLINT. 
FLiNT-nodules_, it appears, owe their origin to sponges. 
These last are animal in their nature, their interior being 
cellular, and on their exterior exist numerous animalcules, 
having cilia, by means of which they create a current in the 
water, and thus obtain food. In the lapse of ages these have 
died, and their cells have become filled up with silex, once 
held in solution in the waters of the ocean. 
If we revert back in imagination to the period when these 
flints were formed, we see the floor of the ocean abundantly 
peopled with marine creatures. There were star-fishes, 
echinites, madrepores, and infusoria; but the sponges were, 
perhaps, the most numerous. Consisting of silica, with a 
very perishable organized tissue, these w’ere ready at any 
time to undergo petrifaction, if circumstances were favorable. 
Bring two globules of mercury near to each other, and see 
how readily they run together into one mass. There you 
have a mechanical example of the way in w hich silica was 
precipitated from the water, and aggregated into nodules 
about the spiculae of the sponges, and by degrees filled up 
the whole skeleton, preserving its form, but destroying its 
substance, and thus changing sponges into nodules of flint. 
Mr. Brande has imitated this very process in experiment, 
and has seen the formation of flinty nodules about a nucleus, 
when finely pow’dered silica has been mixed wdth other 
earths, and the w^hole diffused through w^ater. Every separate 
sponge offering a separate nucleus, suffices to explain why 
flints should commonly appear, as they do, with such de¬ 
cided individuality of character; they are petrified sponges, 
formed in much the same way as those petrified forests 
travellers tell us of, where the trees are all flint; the woody 
fibre has disappeared, but the original structure is still 
traceable in the mass of silex in w’hich the perished organisms 
are now represented. That silica abounded in the seas of 
the period in wffiich the chalk beds were deposited is certain ; 
. but w^e are far from having arrived at a clear idea as to the 
chemistry of the wffiole subject to which flints introduce us. 
We can see the sponges in the flint, and the flint in the 
sponges, and the more w^e observe, reason, and compare, the 
more are we convinced of their geological and chemical re¬ 
lations. 
