In Southern Australia and in New Zealand, the marine shells which lived during the earlier and middle Tertiary times belong to genera and species which are indicative of a warmer climate than that now prevailing; this ancient fauna being like that met with in dredging around the northern coasts of Australia (Fig. 10.) [Illustration: =Fig. 10.--A Fossil Shell (Pecten murrayanus, Tate).= Of Oligocene to Lower Pliocene Age in Southern Australia; closely allied to, if not identical with, a species living off the coast of Queensland. About nat. size. (_F.C. Coll._) ] From the above evidence we may say that:-- _2.--Fossils teach us that in Former Times the Climate of certain parts of the earth's surface was Different from that now existing._ =Fossils as Guides to Age of Strata.--= In passing from fossil deposits of fairly recent origin to those of older date, we find the proportion of living species gradually diminish, being replaced by forms now extinct. After this the genera themselves are replaced by more ancient types, and if we penetrate still deeper into the series of geological strata, even families and orders of animals and plants give place to others entirely unknown at the present day. From this we conclude that:-- _3.--Fossil Types, or Guide Fossils, are of great value in indicating the Relative Age of Geological Formations._ =Gradual Evolution of Life-forms from Lower to Higher Types.--= As a general rule the various types of animals and plants become simpler in organisation as we descend the geological scale. For example, in the oldest rocks the animals are confined to the groups of Foraminifera, Sponges, Corals, Graptolites, Shell-fish and Trilobites, all back-boneless animals: whilst it was not until the Devonian period that the primitive fishes appeared as a well-defined group; and in the next formation, the Carboniferous Series, the first traces of the Batrachians (Frog-like animals) and Reptiles are found. Birds do not appear, so far as their remains are known, until near the close of the Jurassic; whilst Mammals are sparsely represented by Monotremes and Marsupials in the Triassic and Jurassic, becoming more abundant in Cainozoic times, and by the Eutheria (Higher Mammals) from the commencement of the Eocene period. It is clear from the above and other facts in the geological distribution of animal types that:-- _4.--The Geological Record supports in the main the Doctrine of Evolution from Simpler to more Complex types; and fossils throw much light upon the Ancestry of Animals and Plants now found Living._ CHAPTER II. THE CLASSIFICATION OF FOSSIL ANIMALS AND PLANTS. An elementary knowledge of the principles underlying the classification of animals and plants is essential to the beginner in the study of fossils. =The Naming of Animals.--=