HOLLOW LANE. 155 
nautilus. I said that it was in a deep sea the chalk formed: 
this also the naturalist deduces from the fossils; the terebratula 
so common in it is never found in shallow water. 
A few words about the ind of sediment of which our rocks are 
formed. The absence of colour is peculiar and would strike us 
at once, White mud seems almost an anomaly, yet it exists even 
at the present day: there is a certain tract of sea among the 
Bermudas, from the bottom of which it can be dredged up. 
When dry it is undistinguishable from common chalk; it is found 
to consist of carbonate of lime, and to have been formed by in- 
numerable shells of foraminiferee and other minute beings. We 
apply the same tests to our own chalk and we get the same 
results: hosts of delicately-sculptured shells, entire as well as 
broken, come to view beneath the microscope, and we are irre- 
sistibly drawn to the conclusion that nearly the whole of the 
chalk is formed of the shells of animals. The astonishment that 
attends this conclusion increases when we endeavour to think 
only of the number required to form this tract of land here before 
us ; the mind refuses to enter into the calculation when we include 
all the chalk districts known in the world. In this chalk we 
find the remains of corals and sponges plentiful, along with sea 
urchins, fish occasionally and their scattered teeth, but no plants 
except seaweed, no river or land shells, no sand or pebbles— 
everything in fact tends to prove that the deposit was in a deep 
sea, far from land, the climate hot, and the living beings very 
different to what they are now in Europe. 
It is hardly safe to venture a few words on the origin of flints, 
and the cause of their regular stratification. They are found 
most plentifully in the upper chalk, and their composition is sili- 
ceous, not calcareous. I may however say, that it has been dis- 
covered that certain microscopic infusoria may and do produce 
great quantities of flint: many species of sponges have their 
skeletons formed of it, and it would seem that the siliceous parti- 
cles in the neighbouring waters congregated round a sponge as a 
centre, and then by some chemical process became the hardened 
flint stone we now see. It is very certain that the flint was once 
