20 
COLE : CHALK OF YOliKSHlRE. 
The foregoing observations, meagre as they are, do not 
account for the large masses of tabular flint, though they may 
help to explain the origin of nodular flints. What can we say 
more ? only this, that just as calcareous foraminifera are contri- 
buting by their decay to form the ooze of the Atlantic, as, in 
times gone by, they mainly formed the Chalk, so another class of 
life, the siliceous diatoms are busily engaged, at great depths, in 
secreting flint. Hence these may possibly form beds of flint. 
But it cannot be denied that this is an unsatisfactory expla- 
nation^ for beds of tabular flint occur in the middle of the chalk, 
deposited, as presumed above, at no great depth. Bearing, however, 
the fact in mind, that flint may be formed during the decay of 
vegetable matter, may it not be that tabular flints mark areas of 
greater or less extent, where masses of dead seaweed were 
accumulated ? 
The only argument to be urged against this hypothesis is, 
that dead seaweed is mostly washed up on a shore line. But 
what, if these areas were shore lines, or, in other words, surfaces 
of coral reefs ? and what know we how much may settle at 
moderate depths out at sea ? our contention throughout being that 
chalk was not formed in a deep, but in a shallow sea. 
A word more must be added on banded flints ; banded flints 
are not infrequent in the chalk. They resemble agates in showing 
concentric rings of silica of different alternate colours, and clearly 
point to a nucleus of attraction, round which layers of flint ac- 
cumulated, much the same as stalactites are formed by successive 
coatings of liberated carbonate of lime. 
At the recent meeting of the British Association at York, 
(1881) bottles containing sihca in gelatinous forms, into which 
certain solutions of metallic salts had been introduced, were ex- 
hibited, showing in a beautiful manner how, in course of time, 
agates and banded flints might be produced, but the difficulty 
presented itself at once, that silica in a gelatinous form is not 
