THE ANCIENT LIFE-HISTORY OF THE EARTH A COMPREHENSIVE OUTLINE OF THE PRINCIPLES AND LEADING FACTS OF PALÆONTOLOGICAL SCIENCE BY H. ALLEYNE NICHOLSON M.D., D.SC., M.A., PH. D. (GÖTT), F.R.S.E, F.L.S. PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF ST ANDREWS PREFACE. The study of Palæontology, or the science which is concerned with the living beings which flourished upon the globe during past periods of its history, may be pursued by two parallel but essentially distinct paths. By the one method of inquiry, we may study the anatomical characters and structure of the innumerable extinct forms of life which lie buried in the rocks simply as so many organisms, with but a slight and secondary reference to the _time_ at which they lived. By the other method, fossil animals are regarded principally as so many landmarks in the ancient records of the world, and are studied _historically_ and as regards their relations to the chronological succession of the strata in which they are entombed. In so doing, it is of course impossible to wholly ignore their structural characters, and their relationships with animals now living upon the earth; but these points are held to occupy a subordinate place, and to require nothing more than a comparatively general attention. In a former work, the Author has endeavoured to furnish a summary of the more important facts of Palæontology regarded in its strictly scientific aspect, as a mere department of the great science of Biology. The present work, on the other hand, is an attempt to treat Palæontology more especially from its historical side, and in its more intimate relations with Geology. In accordance with this object, the introductory portion of the work is devoted to a consideration of the general principles of Palæontology, and the bearings of this science upon various geological problems--such as the mode of formation of the sedimentary rocks, the reactions of living beings upon the crust of the earth, and the sequence in time of the fossiliferous formations. The second portion of the work deals exclusively with Historical Palæontology, each formation being considered separately, as regards its lithological nature and subdivisions, its relations to other formations, its geographical distribution, its mode of origin, and its characteristic life-forms.