As we grope our way backward through the dark labyrinth of the ages, epoch succeeds to epoch, and period to period, each looming more gigantic in its outlines and more shadowy in its features, as it rises, dimly revealed, from the mist and vapour of an older and ever-older past.

It is useless to add century to century or millennium to millennium.

When we pass a certain boundary-line, which, after all, is reached very soon, figures cease to convey to our finite faculties any real notion of the periods with which we have to deal.

The astronomer can employ material illustrations to give form and substance to our conceptions of celestial space; but such a resource is unavailable to the geologist.

The few thousand years of which we have historical evidence sink into absolute insignificance beside the unnumbered aeons which unroll themselves one by one as we penetrate the dim recesses of the past, and decipher with feeble vision the ponderous volumes in which the record of the earth is written.