class="right">244.

Hippopotamus Sivalensis. 245. Skull of Sivatherium. 246. Skull of Deinotherium. 247. Tooth of Elephas planfrons and of Mastodon Sivalensis. 248. Jaw of Pliopithecus. 249. Rhinoceros Etruscus and R. megarhinus. 250. Molar tooth of Mastodon Arvernensis. 251. Molar tooth of Etephas meridionalis. 252. Molar tooth of Elephas antiquus. 253. Skull and tooth of Machairodus cultridens. 254. Pecten Islandicus. 255. Diagram of high-level and low-level gravels. 256. Diagrammatic section of Cave. 257. Dinornis elephantopus. 258. Skull of Diprotodon. 259. Skull of Thylacoleo. 260. Skeleton of Megatherium. 261. Skeleton of Mylodon. 262. Glyptodon clavipes. 263. Skull of Rhinoceros tichorhinus. 264. Skeleton of Cervus megaceros. 265. Skull of Bos primigenius. 266. Skeleton of Mammoth. 267. Molar tooth of Mammoth. 268. Skull of Ursus spelœus. 269. Skull of Hyœna spelœa. 270. Lower jaw of Trogontherium Cuvieri.

PART I.

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PRINCIPLES OF PALÆONTOLOGY.

THE
ANCIENT LIFE-HISTORY
OF
THE EARTH

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INTRODUCTION.

THE LAWS OF GEOLOGICAL ACTION.

Under the general title of "Geology" are usually included at least two distinct branches of inquiry, allied to one another in the closest manner, and yet so distinct as to be largely capable of separate study. Geology,[1] in its strict sense, is the science which is concerned with the investigation of the materials which compose the earth, the methods in which those materials have been arranged, and the causes and modes of origin of these arrangements. In this limited aspect, Geology is nothing more than the Physical Geography of the past, just as Physical Geography is the Geology of to-day; and though it has to call in the aid of Physics, Astronomy, Mineralogy, Chemistry, and other allies more remote, it is in itself a perfectly distinct and individual study. One has, however, only to cross the threshold of Geology to discover that the field and scope of the science cannot be thus rigidly limited to purely physical problems. The study of the physical development of the earth throughout past ages brings us at once in contact with the forms of animal and vegetable life which peopled its surface in bygone epochs, and it is found impossible adequately to comprehend the former, unless we possess some knowledge of the latter. However great its physical advances may be, Geology remains imperfect till it is wedded with Palæontology,[2] a study which essentially belongs to the vast complex of the Biological Sciences, but at the same time has its strictly geological side. Dealing, as it does, wholly with the consideration of such living beings as do not belong exclusively to the present order of things, Palæontology is, in reality, a branch of Natural History, and may be regarded as substantially the Zoology and Botany of the past. It is the ancient life-history of the earth, as revealed to us by the labours of palæontologists, with which we have mainly to do here; but before entering upon this, there are some general questions, affecting Geology and Palæontology alike, which may be very briefly discussed.

[Footnote 1: Gr. ge, the earth; logos, a discourse.]

[Footnote 2: Gr. palaios, ancient; onta, beings; logos, discourse.]

The working geologist, dealing in the main with purely physical problems, has for his object to determine the material structure of the earth, and to investigate, as far as may be, the long chain of causes of which that structure is the ultimate result. No wider or more extended field of inquiry could be found; but philosophical geology is not content with this. At all the confines of his science, the transcendental geologist finds himself confronted with some of the most stupendous problems which have ever engaged the restless intellect of humanity. The origin and primæval constitution of the terrestrial globe, the laws of geologic action through long ages of vicissitude and development, the origin of life, the nature and source of the myriad complexities of living beings, the advent of man, possibly even the future history of the earth, are amongst the questions with which the geologist has to grapple in his higher capacity.

These are problems which have occupied the attention of philosophers in every age of the world, and in periods long antecedent to the existence of a science of geology. The mere existence of cosmogonies in the religion of almost every nation, both ancient and modern, is a sufficient proof of the eager desire of the human mind to know something of the origin of the earth on which we tread. Every human being who has gazed on the vast panorama of the universe, though it may have been but with the eyes of a child, has felt the longing to solve, however imperfectly, "the riddle of the painful earth," and has, consciously or unconsciously, elaborated some sort of a theory as to the why and wherefore of what he sees. Apart from the profound and perhaps inscrutable problems which lie at the bottom of human existence, men have in all ages invented theories to explain the common phenomena of the material universe; and most of these theories, however varied in their details, turn out on examination to have a common root, and to be based on the same elements. Modern geology has its own theories on the same subject, and it will be well to glance for a moment at the principles underlying the old and the new views.

It has been maintained, as a metaphysical hypothesis, that there exists in the mind of man an inherent principle, in virtue of which he believes and expects that what has been, will be; and that the course of nature will be a continuous and uninterrupted one. So far, however, from any such belief existing as a necessary consequence of the constitution of the human mind, the real fact seems to be that the contrary belief has been almost universally prevalent. In all