Palaeontology (named from the Greek palaios, "ancient"; onta, "beings"; logos, "science") is the science of fossils (q.v.). In its method it is largely a distinct science; but in its results it may be considered as the contribution of geology (q.v.) to biology (q.v.). Owing to the merely partial preservation of their remains, fossil plants and animals are studied from somewhat different points of view from those of which flowers or muscles are still available ; and, whilst all existing plants and animals are contemporaneous, one of the chief interests in the study of fossils arises from their presenting to us a succession, the floras and faunas of successive past periods of the earth's history. Fossil organisms not only add large numbers of species and genera to those now known as living on the globe; but many of them belong to extinct types, some of which are generalised, or combine the characters of groups which have since become distinct, and may, therefore, well be looked upon as ancestral. Though there is abundant evidence of a general succession, or advance of organic types, the lower in organisation being, on the whole, the earlier in appearance in time, there is still a great imperfection of the palaontological record. Thus we have no geological evidence as to the beginnings of life on the globe, the earliest known assemblage of fossils, that in the Lower Cambrian (q.v.), containing representatives of nearly all classes of invertebrate animals. Again, though in many groups, as, for instance, among ungulate mammals, there are now known a large graduating series of genera; in this and in many other groups it is impossible to point to the minute inter-gradation of species which would seem to be required by the theory of natural selection. In other groups, however, such as the brachiopods, the ammonites, and the whelks, such an inter-gradation can be fairly well shown. This imperfection of the record arises in part from the as yet incomplete investigation of our fossiliferous rocks; but also from the destruction by denudation of such rocks once in existence; from the obliteration of the fossils in others, as by percolating water or crystallisation due to heat; or, still more, from the scant chance of preservation as fossils of the remains of plants and animals dying at a distance from water and its preserving mud. These latter causes render many of the gaps in our knowledge irremediable. Nevertheless, Sir A. Geikie expresses the opinion that "it must be conceded that, on the whole, the testimony of the rocks is in favour of the doctrine of evolution."