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this free sarcode was detected, tlie occurrence of Flints in some 
localities in the form of nodules, and in others as layers, was 
difficult to account for, but when it was found that sarcode existed 
in masses covering a considerable area, a clue to the formation of 
the flint layers became apparent. Carbonic acid gas, and hydrogen 
were liberated when decomposition set in, and silex replaced the 
sarcode. That Flints are now forming, is, I think, as certain as 
the formation of new beds of chalk, and it is an ascertained fact, 
that the valleys in the bed of the ocean, are, as in days of yore, 
being gradually filled with calcareous matter intermingled with 
remains of sponges, or permeated with protoplasm, these as decom- 
position slowly takes place are separating the silica from the sur- 
rounding waters. 
It wilt, I think, be allowed, that flint nodules could not have 
been found in chalk unless a nucleus had existed, the silica con- 
tained in the water was chemically combined with it, the chalk 
only mechanically, and if any silica was parted with it would only 
act as silicious cement hardening the atoms of chalk. 
Ihe probability that Flints are still in the jirocess of formation, 
is confirmed by the frequent discovery of silicious casts of forami- 
nifera, those usually found are composed of silex with traces of 
mon, giving them an olive green colour, precisely like those found 
in the green sand. 
In a dredging made at Porto Segiiro by Capt. Perry, of Liver- 
pool, I found many shells of foraminifera, which when acted upon 
by acid, showed the interior flUed with a silicious cast of the 
internal chambers, and in some specimens even the pseudo-podal 
apei'tures had also been filled with silex, fragments of other silicified 
organisms were also of frequent occurrence. The casts found in 
this dredging differed from those usually found by the absence of 
any trace of iron, and appeared to be silica in a similar condition 
to the ordinary chalk Flint. 
In the green sand large silicious nodules, known as Polypothecia 
are of frequent occurrence, and when thin sections are examined 
their spongeous origin is distinctly seen; these nodules were, 
however, formed under somewhat different conditions to the ordi- 
nary chalk Flint, the silica is distinctly crystalline and doubly 
refractive, and polarizes like quartz or agate ; the sponges were 
also probably different from those belonging to the chalk ; a careful 
