Observation, then, establishes the truth of the explanation we have
given concerning the formation of the chalky or Cretaceous rocks; but
the question still remains--How did these rocks, originally deposited in
the sea, become elevated into hills of great height, with bold
escarpments, like those known in England as the North and South Downs?
The answer to this involves the consideration of other questions which
have, at present, scarcely got beyond hypothesis.
[Illustration: Chalk under the Microscope.