extracts of more important parts, with some criticisms, in the Geological Magazine (N.S., sec. iv., vol. iv., 1897). I freely acknowledge the value of these criticisms, which have largely assisted me to amplify and to improve upon the ideas laid down in the paper.

I have found that it greatly facilitates comprehension of the arguments used, to give a few maps indicating in a general way the extent of former seas and continents. I may in this way, as Mr. Kendall has pointed out, have submerged many square miles of land which had never been covered by the sea,—at least not within recent geological times,—but the maps were intended as illustrations of my views in a broad spirit only.

Some zoologists may be surprised that, in some cases, I have not followed the latest views in revised nomenclature. I felt that in a work of this kind it was of supreme importance to employ names still current in our leading text-books, such as Lepus variabilis for the Mountain Hare, instead of Lepus timidus. After each chapter I have endeavoured to give a short summary of contents, while a bibliography of the principal works and papers consulted will be found at the end. I should also acknowledge the aid which I have received from such excellent works of reference as the British Museum Catalogues of Birds, by Dr. Bowdler Sharpe, and those of Reptiles, Amphibia, and Fishes, by Dr. Günther and Dr. Boulenger. The valuable works on Mammalia by Sir W. Flower, Mr. Lydekker, Mr. Grevé, and Dr. Trouessart, were indispensable to me.

To Sir William Flower, Mr. Lydekker, Professor Sars, and Professor Smitt, I am especially indebted for allowing me to reproduce drawings from their works, and to my friend Mr. Welch for some beautiful photographs. The Council of the Royal Irish Academy also kindly gave me permission to reprint the maps used in illustration of my paper. Professor Haddon first suggested my writing this book, and gave me many useful hints; and great assistance was rendered me by my colleague, Mr. G. H. Carpenter, in revising the proofs. To both of these kind friends I desire to acknowledge my deep sense of gratitude.

R. F. SCHARFF.

THE HISTORY OF THE
EUROPEAN FAUNA.

CHAPTER I.
INTRODUCTION.

Every student of natural history, whether he be interested in birds, butterflies, or shells, contributes his share of facts which help to show how the fauna of his country has originated. The capture of a Swallow-tail or of a Marbled White Butterfly in England at once furnishes material for reflection as to the reason of its absence from Scotland and Ireland. Why should the Nightingale allow its beautiful song to be heard in England, and never stray across the Channel to the sister isle or cross the borders of North Britain? Lovers of bird-life and sportsmen, who have observed the habits of the Ptarmigan in the wild mountain recesses of Scotland, are aware that nowhere else in the British Islands do we meet with this interesting member of the grouse family, and many no doubt have allowed their minds to dwell upon the causes of its singularly local distribution.

All these animals have a wide range in other parts of the world. In past times, before man began to make observations on the geographical distribution of birds and butterflies, or even before the appearance of man in Northern Europe, they may have lived all over the British Islands. For some reason or other they are perhaps dying out or withdrawing towards their original home, which may either be northward, or to the east or south. If we had some clue as to their former history from fossil evidence—or, in other words, if their remains had been preserved to us in geological deposits,—we should have less difficulty in deciding this problem. But butterflies are scarcely ever preserved in a fossil state, and birds very rarely. We know little or nothing, therefore, of their past history from direct evidence, and are obliged to trust to indirect methods of research which will be indicated later on.

Mammals and Snails tell us their story more plainly. The bones of the former and the shells of snails are easily preserved, and thus furnish us with the necessary data as to their past history, for we find them abundantly in most of the recent geological deposits. Among the mammals of the British Islands there are some instances of distribution which much resemble those I have quoted. Thus the Arctic Hare (Lepus variabilis) is in the British Islands confined to Ireland and to the mountains of Scotland; and if it were not for the fact that its bones have been discovered in a cave in the south-west of England, we should perhaps never have known that, formerly, it must have inhabited that country as well. Of other mammals we possess fossil and also historical evidence of their having once lived in these islands. Such are the Wolf and the Wild Boar, both of which were abundant in Great Britain and Ireland. The latter is a distinctly southern species. We assume this, because its remains have never been found in high northern latitudes; nor does it now occur in Northern Europe or Northern Asia, whilst all its nearest relatives live in sub-tropical or tropical climates. The Arctic Hare, on the contrary, has probably come to us from the north. Its remains are unknown even in Southern Europe, and the more we approach the Arctic Regions, the more abundant it becomes. Thus we have here two instances of British mammals, one of which, the Wild Boar, has died out—as it were in a southerly direction; whilst the other, the Arctic Hare, is apparently retreating towards the north.

There are also some British mammals of which we have no fossil history, at least of which no remains have as yet been found in these islands. Such a one is the Harvest Mouse (Mus minutus). It has a somewhat restricted range in England, and only just crosses the Scottish border in the east. From the rest of Scotland and from the whole of Ireland it is absent. To judge from this distribution, in connection with the fact of its being unknown as a British fossil species, it is probably a late immigrant to England, and has not had time to spread, throughout Scotland at any rate. But it is also absent from Scandinavia, from the Spanish peninsula, from almost the whole of Italy and the Alps, as also from the Mediterranean Islands, whilst the little mouse occurs abundantly right across Siberia. We shall learn more about centres of dispersion later on; meanwhile I should mention that such a distribution indicates that the Harvest Mouse has most likely originated in the east, and has spread from there westward in recent geological times.

Conchologists have long ago been acquainted with the fact that many molluscs, for example the so-called "Stone-cutter" Snail (Helix lapicida) and the "Cheese Snail" (Helix obvoluta), have a very restricted range in the British Islands. Both are entirely absent from Scotland and Ireland, the Cheese Snail being confined to South-eastern England. The Stone-cutter has rather a wider range, is even known from a Welsh locality, and is met with as far north as Yorkshire. Their distribution would indicate, therefore, that while both are recent immigrants, the Cheese Snail is probably the last comer. This supposition is in so far supported by fossil evidence, as the latter is unknown in the fossil state, whilst the Stone-cutter has been described by Messrs. Kennard and Woodward (p. 243)[1] as occurring in