The science of the earth as illustrated by geological research, is one of the noblest outgrowths of our modern intellectual life. Constituting the sum of all the natural sciences in their application to the history of our world, it affords a very wide and varied scope for mental activity, and deals with some of the grandest problems of space and time and of organic existence. It invites us to be present at the origin of things, and to enter into the very workshop of the Creator. It has, besides, most important and intimate connection with the industrial arts and with the material resources at the disposal of man. Its educational value, as a means of cultivating the powers of observing and reasoning, and of accustoming the mind to deal with large and intricate questions, can scarcely be overrated. But fully to serve these high ends, the study of geology must be based on a thorough knowledge of the subjects which constitute its elementary data. It must be divested as far as possible of merely local colouring, and of the prejudices of specialists. It must be emancipated from the control of the bald metaphysical speculations so rife in our time, and above all it must be delivered from that materialistic infidelity, which, by robbing nature of the spiritual element, and of its presiding Divinity, makes science dry, barren, and repulsive, diminishes its educational value, and even renders it less efficient for purposes of practical research. That the want of these preliminary conditions mars much of the popular science of our day is too evident; and I confess that the wish to attempt something better, and thereby to revive the interest in geological study, to attract attention to its educational value, and to remove the misapprehensions which exist in some quarters respecting it, were principal reasons which induced me to undertake the series of papers for the _Leisure Hour_, which are reproduced, with some amendments and extension, in the present work. How far I have succeeded, I must leave to the intelligent and, I trust, indulgent reader to decide. In any case I have presented this many-sided subject in the aspect in which it appears to a geologist whose studies have led him to compare with each other the two great continental areas which are the classic ground of the science, and who retains his faith in those unseen realities of which the history of the earth itself is but one of the shadows projected on the field of time.