Ornithologists are well acquainted with the fact that in some years there is an unusually large exodus from Eastern Europe and Siberia of birds; and that species like the Waxwing (_Ampelis garrulus_) then appear in great numbers. But the appearance of this bird in Western Europe is not looked upon as so remarkable as that of Pallas's Sandgrouse (_Syrrhaptes paradoxus_, Fig. 3, p. 42), a typical inhabitant and resident of the Arctic Steppes. The last great irruption took place in 1888, and many birds reached even the extreme west of Ireland in May and June of that year. A few weeks before, it had been announced to the German papers that large flocks of this peculiar pigeon-like bird had arrived in the eastern provinces; and though the vast majority vanished as quickly as they had come, a certain number remained for a year or so in the newly visited countries, and some even bred in England. Twenty-five years before, in 1863, a similar migration had occurred, though not perhaps on quite such a vast scale, and a few small flocks had made their appearance in Western Europe on several occasions between these dates. It may not be generally known that no other bird has been honoured by our Government in a like manner, for it is the only animal for whose protection a separate Act of Parliament has been passed. In spite of this unusual precaution, the species has not survived to add another member to the resident British fauna. The wave of migration from the east has come and vanished again just like so many others with which history is familiar. These migrations from the east occurring at the present day give us some idea of those of which we have fossil evidence, and which all had their origin in Central and Northern Asia. Almost all the species of mammals to which I have referred as being of Siberian origin have been found in the fossil state in comparatively recent geological deposits within a certain very limited area. None of the typical species have ever been found in Southern Europe proper, including the Mediterranean islands. It must be remembered that though the Reindeer is a Siberian migrant, the form of the Reindeer which was found in the Pyrenees belonged to a distinct variety--in fact, to a much earlier migration which issued from the Arctic European Regions, and to which I have referred in detail (pp. 150-158). Curiously enough, no deposits of these typical Siberian mammals have ever been obtained in Scandinavia--only in Russia, Austria, Switzerland (the lowlands), Germany, Belgium, France, and England. To facilitate a study of the extent of these migrations, I have constructed a map on which the probable course taken across Central Europe is roughly indicated by dots (Fig. 16). [Illustration: Fig. 16.--Map of Europe. The dotted portions represent, approximately, the course of migration of the Siberian mammals. The principal mountain ranges are roughly indicated in black.]