This could only be true if the time taken for the migration of faunas and floras was so great as to transcend the boundaries between great geological periods. This does not appear to be the case, and Huxley's idea in its extreme form has been generally abandoned. At the same time certain anomalies in the range in time of individual genera have been noted, and may possibly be explained on such lines. For instance, among the group of the graptolites, in Britain the genus _Bryograptus_ occurs only in the Upper Cambrian and the genus _Leptograptus_ only in the Upper Ordovician rocks. In Victoria these two genera, together with typical Lower Ordovician forms, may be found near Lancefield preserved on a single slab of shale. In the same way, in a single quarry in Triassic rocks in New South Wales, a number of fossil fish have been found and described, some of which have been compared to Jurassic, others to Permian, and others to Carboniferous forms in the Northern Hemisphere. Another point which the palaeontologist may occasionally find evidence for is the existence of "biological asylums," areas which by means of land or other barriers may be for a long period separated from the main stream of evolution. We know that the present fauna and flora of Australia is largely of archaic aspect, as it includes a number of types which elsewhere have long ago become extinct or were never developed. This appears to be due to the long isolation of Australia and, as Professor Gregory happily puts it--its "development in a biological backwater." We have some evidence that similar asylums have existed in past geological periods, with the result that in certain areas where uniform conditions prevailed for a long time or where isolation from competition prevented rapid evolution, some organisms which became extinct in other areas, persisted unchanged in the "asylum" into a younger geological period. The broad generalizations that rocks may be identified by their fossil contents and that the testimony of the rocks demonstrates the general order of evolution from simple to complex forms, have only been placed on a surer footing by long continued investigations. The modifications produced by conditions of deposit, of climate and of natural barriers to migration, while introducing complexities into the problems of Palaeontology, are every year becoming better known; and when considered in connection with the variations in the characters of the rocks, provide valuable and interesting evidence towards the solution of the ultimate problems of geology and palaeontology, which include the tracing out of the evolution of the history of the earth from the most remote geological period to that point at which the geologist hands over his story to the archaeologist, the historian, and the geographer. ERNEST W. SKEATS. PART I. GENERAL PRINCIPLES. CHAPTER I. NATURE AND USES OF FOSSILS. =Scope of Geology.--=