PREFACE.

THE object of the following Chapters is to present a sketch in outline of the World's Life-System-tracing from the earliest organisms in the stratified crust to the forms that now adorn and people its surface. The aim has been to link the remote to the recent-the living to the extinct-that the general reader may be enabled to form some intelligible conception of the whole as a great and continuously-evolving scheme of vegetable and animal existences. There is no attempt whatever to teach anatomical details or point out specific distinctions-the volume being intended not as a Handbook of Palæontology, but simply as a readable sketch for the information of those who have neither the time nor the preliminary training to avail themselves of works of higher scientific pretensions. And yet the reader will find in these pages a reliable résumé of the science, as founded on the most recent discoveries, and a treatment of its bearings from a higher stand-point than can be conveniently taken by the mere text-books and manuals of Geology. At a time

when the question of Life is receiving a wider audience, such a résumé may also be of utility in indicating the line that separates the assumed and hypothetical from the known and ascertainable; and so prevent the unprofessional inquirer from ascribing to Geology what it does not affirm, or from expecting from its teachings what they cannot reveal.

Designed for the general reader, and delivered in part to popular audiences, the style is, perhaps, somewhat more rhetorical than befits the exactitudes of science; but even on this point the Author could not well have done otherwise. His object was to excite rather than satisfy the curiosity of his hearers-to impress them with the universality and uniformity of natural law-believing there can be no true notion of Nature or of Nature's requirements while her facts are viewed through the medium of the miraculous. Nor let it be thought that, by recognising in every instance the fixity and unerring operation of Law, we place a wider distance between the Creator and his works, or that any knowledge of this kind has a tendency to self-sufficiency or irreverence. On the contrary, he who knows most of creational law, and that the most intimately, stands generally the least in need of the injunction-" Put off thy shoes from off thy feet, for the place whereon thou treadest is holy."

In treating such a theme as Life-its apparent origin and progress-the writer has necessarily had occasion

to allude to subjects on which there is much diversity of opinion; to some that are usually approached with uneasy tenderness, as coming in conflict with prevalent beliefs; and to others on which the united labours of Geologists, during the last fifty years, have thrown but little reliable light or information. In either case he has expressed his opinions freely, but without dogmatism; firmly, but solely under the warrant of Geology; and always with a frank admission of the many deficiencies and imperfections of that science. As there is nothing to be gained by offending a prejudice where we cannot establish a conviction, he has contented himself by stating what Geology affirms, without alluding to what it appears to contradict; and as the establishment of truth does not always follow the overturning of error, the expounder of science may surely be permitted to attempt the one without hazarding an endeavour to accomplish the other. In approaching our subject, therefore,-a subject too often treated as if it lay beyond the pale of natural law,- let it be clearly understood that we are dealing with Life solely in its geological aspects. We appeal unto Cæsar; let us be judged by Cæsar's laws.

GILMORE PLACE, EDINBURGH,

February 1861.