But we have no reason to assume that things have thus remained from the beginning of the world.

Our continents seem to have been formed by a preponderance, during many oscillations of level, of the force of elevation.

But may not the areas of preponderant movement have changed in the lapse of ages? At a period long antecedent to the Cambrian epoch, continents may have existed where oceans are now spread out, and clear and open oceans may have existed where our continents now stand.