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most important element in his problem. He alludes to the food of the forami- 
nifera. Now, part of that food must be of a peculiar character. The shells 
of these foraminifera which form the chalk are made up of carbonate of lime. 
That carbonate of lime must have been in solution in the water in order that 
they might assimilate it and form it into shell. The only form, so far as we 
know, in which carbonate of lime can be thus assimilated from water, is its 
solution in carbonic acid. As carbonate of lime dissolved in carbonic acid, 
then, must all the chalk have first existed in the water before the foraminifera 
could appropriate it to form their shells. But here we have at once a limit 
to their multiplication. Directly the carbonate of lime falls off, their growth 
and increase must fall off too. Now, the quantity of carbonate of lime which 
water, even when saturated with carbonic acid, is capable of holding in solu- 
tion is but small. Even supposing the whole sea to be thus saturated, only 
a thin crust of carbonate of lime would be formed by the removal of the 
carbonic acid. Nor, if the deposition of the carbonate of lime took place 
through the agency of foraminifera, would the amount of rock so formed be 
any greater. The carbonate of lime thus removed, the increase of forami- 
nifera would be altogether stopped, except a fresh supply could be obtained. 
This supply cannot arise from the solution of fresh carbonate of lime within 
the sea itself, because if there be free carbonic acid sufficient for this 
end it would dissolve, not only any limestone that might be there, but also 
the shells of the dead foraminifera themselves, and thus in another way put 
a stop to their accumulation. Whence, then, can the supply come ? It can 
come certainly from the rivers, which are constantly bearing down carbonate 
of lime in solution into the sea. But, then, the supply from this source is 
very small as compared with the bulk of chalk to be formed. Taking all 
these points into consideration, it seems to me utterly incredible that the 
vast masses of chalk now in existence could have been formed in the time, 
or anything like the time, that Mr. Mitchell is disposed to allow. Had I 
known that the point was coming up in the paper to-night, I would have gone 
into the matter more exactly, but as it is, I am of course only able to deal 
with it roughly and in general terms. 
Professor Macdonald. — Am I to suppose that Mr. Mitchell objects to 
the successive creation theory 1 
Mr. Mitchell. — I have only given what Sir Charles Lyell himself says ; 
I have taken him as my authority, and I agree with him that the whole 
evidence of modem geology is tending against the successive theory. 
Professor Macdonald. — I probably may not know what that means, but 
I do not suppose that you maintain that the whole crust of the earth is the 
result of one instantaneous creation ? 
Mr. Mitchell. — I do not say that it was. What is described as the suc- 
cessive creation theory is this (I will take what Professor Huxley himself 
has said), that there are three great divisions — primary, secondary, and ter- 
tiary — and that they indicate three distinct creations. The animals therein — 
the animals of the cretaceous period, for instance — are essentially distinct 
from the animals of the carboniferous period, and so on. 
