Wallich^ on Siliceous Organisms. 
51 
to the same sequence of disintegration and reconstruction 
that had been undergone by every siliceous particle consti- 
tuting the nodule which enveloped it. And imperishable 
though the material^ both in its former and present state^ all 
trace of its exquisite structure had been obliterated ; whilst 
the delicate fabric it once served to support alone remained to 
tell the wondrous history. 
I have alluded in a previous part of this paper to the food 
of the Salpse and other pelagic creatures being composed^ in a 
great measure^ of Diatomacese and other siliceous-walled 
organisms. I have pointed out in what inconceivably vast 
multitudes the Salpse are met with ; and endeavoured to esta- 
blish some relation between the siliceous exuviae of these 
creatures, and, on a yet vaster scale, the exuviae of the 
gigantic cetaceans that feed, in turn, upon the Salpse, 
with the siliceous material to be found in the deep-sea 
deposits. 
But another most important and interesting point demands 
notice. Namely, the extent to which, by these combined 
operations, the siliceous particles may become accumulated 
into masses, either by chemical combination or simple elective 
affinity, so as to account for the layers and nodules of flint 
which occur in the Chalk formMion. 
Few subjects, probably, have given rise to greater difference 
of opinion and discussion than the flints in question. Pro- 
fessor Ehrenberg has stated an opinion that the flint nodules 
and layers of the British Chalk formation have been derived 
by some metamorphic process from strata of Diatomacesc, 
which have disappeared under its action. 
Again, it is believed by some eminent geologists that flints 
are aggregations of silex, round some organic nucleus, such as 
sponges, pieces of coral, shell, and the like ; and that such 
aggregation took place whilst the silex was held in a state of 
solution by the waters of the deposit. But this view can 
hardly be said to account, in a satisfactory manner, for the 
segregation of the siliceous compound into distinct masses and 
layers, such as are to be found m the Chalk formation, and 
which impart to it a degree of stratification. 
Others regard the action as one of molecular affinity. 
^' There appears no evidence,^^ says Mr. Brande, of its {the 
Chalk) having be(?n precipitated from chemical solution ; but, 
on the other hand, it bears marks of a mechanical deposit, as 
if from water loaded with it in a state of fine division. And 
upon this principle, some gleam of light may perhaps be 
thrown upon the enigmatical appearance of the flints ; for 
it is found that if finely powdered .silica be mixed with other 
