Prodigious! says the reader. And so it is. Prodigious to think that
that shallow Greensand shore, strewed with dead animals, should sink
to the bottom of an ocean, perhaps a mile, perhaps some four miles
deep. Prodigious the time during which it must have lain as a still
ocean-floor. For so minute are the living atomies which form the
ooze, that an inch, I should say, is as much as we can allow for
their yearly deposit; and the chalk is at least a thousand feet
thick. It may have taken, therefore, twelve thousand years to form
the chalk alone. A rough guess, of course, but one as likely to be
two or three times too little as two or three times too big. Such,
or somewhat such, is the fact. It had long been suspected, and more
than suspected; and the late discoveries of Dr. Carpenter and Mr.
Wyville Thompson have surely placed it beyond doubt.
Thus, surely, if we call the Oolitic beds one new world above the New
Red sandstone, we must call the chalk a second new world in like
wise.
I will not trouble the reader here with the reasons why geologists
connect the chalk with the greensands below it, by regular
gradations, in spite of the enormous downward leap, from sea-shore to
deep ocean, which the beds seem (but only seem) to have taken. The
change--like all changes in geology--was probably gradual.
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