of animals since the post-pliocene times, and either just before or shortly after the appearance of man. This phenomenon was apparently simultaneous in Europe and America, and will doubtless be traced in other quarters of the globe when their paleontology has been more fully studied. Among the animals which have thus disappeared are some which seem to have been eminently qualified to "hold their own." Such is the extinct genus Machairodon, or sabretoothed tiger, several fossil species of which, apparently more formidable than any existing cat, have been found in both continents.

Another very important conclusion is, that the theory of the independent origin and development of animal life in a number of distinct points can no longer be upheld. The great northern continents appear to have been the seat and birthplace of all the higher forms of life, whilst certain strange creatures-such as the gigantic fossil Edentataseem to have originated in the south and to have gradually spread northwards.

In one respect we must own ourselves disappointed with Mr. Wallace's book, although the author, in his Address delivered before the Biological Section of the British Association at Glasgow, has done very much to supply the deficiency. We had expected that the work would have contained a summary of facts, and possibly some interesting generalisations on the influence of locality on the colour, the size, and the form of animal species. Every naturalist —save such, if they deserve the name, who confine their researches to books-knows that the fauna of each country. has a peculiar general physiognomy, more or less pronounced. These peculiarities are sometimes difficult to express in words, and may escape any but the most patient observer, but in other instances they are open and palpable. Thus, according to Mr. Goodman, there appear in the birds of the Azores modifications all tending towards a more sombre plumage, and a greater strength of feet, legs, and bill. Mr. Blanford finds that Persian specimens are, on the average, paler in colour than their nearest allies in Europe. Mr. Wallace, in his Glasgow Address, remarks that it is "in islands we find some of the most striking examples of the influence of locality on colour, generally in the direction of paler, but sometimes of darker and more brilliant hues, and often accompanied by an unusual increase of size." He then shows how the butterflies of certain genera, such as the Euplaas, are in the larger islands darkcoloured, whilst in Banda, Ké, and Matabello there are three

species, not nearly related to each other, "all broadly banded or suffused with white." "The small island of Amboyna produces larger-sized butterflies than any of the larger islands which surround it. This is the case with at least a dozen butterflies belonging to many distinct genera."

Corresponding cases of paleness are found in Fiji, in the Andamans, and in Jamaica.

In Celebes, as Mr. Wallace has shown in an earlier work,* instead of any modification of colour, there is "a peculiar form of wing and a much larger size running through a whole series of distinct butterflies."

The Philippine Islands seem to have the property of developing intense metallic lustre, both in butterflies and beetles. Thus the hind wings of Ornithoptera Magellanus "glow with an intense opaline lustre not found in any other species of the entire group, and Adolias calliphorus is larger and of more brilliant metallic colouring than any other species in the Archipelago. In these islands, also, we find the extensive and wonderful genus of weevils, Pachyrhynchus, which in their brilliant metallic colouring surpass anything found in the whole eastern hemisphere, if not in the whole world."

Continental districts likewise have their peculiarities of colouration. Thus two unrelated groups of butterflies from tropical Africa "are characterised by a prevailing blue-green colour not found in any other continent." Similarly, in South America, "nine very distinct genera are implicated in parallel changes, groups of three or four of them appearing in the same livery in one district, while in an adjoining district most or all of them undergo a simultaneous change of colouration or marking."

These local peculiarities may perhaps be overlooked because they occur in insects, but Mr. Wallace very aptly asks-What should we think if similar phenomena were to be traced amongst large mammals?

In birds, however, local characteristics of a corresponding nature occur, as the author proves by reference to the avifauna of the West Indies, the Andamans, the Philippines, Celebes, Timor, Flores, and Lord Howe's Island. In New Guinea, Australia, Madagascar, and the Mascarenes we have black parrots and pigeons-a curious instance of the phenomenon known as melanism.

* Contributions to the Theory of Natural Selection, pp. 168-173.

It has been maintained that, in the Nearctic region at least, the Mammalia increase in size with the latitude and altitude of their birthplace. This view is disputed by Mr. Allen, who declares that it does not agree with the development of the American Carnivora. Indeed as regards altitude, and consequently rarefaction of the ambient medium, the very opposite law has been proposed. The largest animals are now found in the denser medium, water; many of the next largest species-such as the elephants, hippopotamus, &c.—inhabit river-marshes and deltas almost on a level with the sea. There is also good reason for supposing that the atmosphere in the epochs which produced the gigantic extinct animals must have been denser than it is at present. Mr. Allen considers that the largest individuals of every species, and the largest, best-developed, and most typical species of every group, will be found near its centre of distribution.

It has also been suggested, at least as regards insects, that in all regions dark-coloured species are characteristic of woods, whilst white or light-coloured forms occur in the open plains. This law holds good in some well-known genera of butterflies, such as the "whites" as compared with the forest-loving Hipparchias, Erebias, &c.; but the deeply-coloured Vanessas inhabit the open country. Among Coleoptera we find the dung-beetles, mainly black in colour, abundant in the open country, like the ruminants on whose excrement they prey. The common ground-beetles, also (Harpalidæ, &c.), are chiefly sombre in colour, and certainly show no exclusive preference for woods. On the other hand, the chafers (Melolonthida) and the Buprestids frequent the woods, and yet display some of the most striking instances of pale colouration to be found among the entire tribe of Coleoptera.

For further details on the influence of locality we must refer the reader to Mr. Wallace's most instructive Address, but we cannot help expressing our regret that he has not introduced the consideration of this subject into his magnum opus.

We may rest assured that the peculiarities to which we have so briefly referred point to causes of variation at work other than protective mimicry or than sexual selection. This is evidently the opinion of Mr. Wallace, who insists that "one of these causes is an influence depending strictly on locality, whose nature we cannot yet understand, but whose effects are everywhere to be seen when carefully VOL. VII. (N.S.)

F

searched for. If it be asked why so little attention is given to this and to other interesting problems connected with the distribution of organic life, one important cause has been pointed out by Mr. Wallace-the total want of a museum geographically arranged. Our museums, more or less complete, are arranged morphologically. Birds, reptiles, insects, &c., which approximate in their structure are placed together, quite irrespective of the locality from which they have been obtained. Such collections are obviously indispensable, and all we recommend concerning them is that they should be made much more complete and more accessible than is now the case, and should invariably be placed in some central position, and not in a remote, even though fashionable, suburb. But along with such we want also a museum geographically arranged, where we may see, c.g., in one hall the fauna of India, in another that of New Guinea, of Australia, of Madagascar, or of the Cape. Who can doubt that if such collections were accessible, relations, similarities, contrasts would strike us which escape unnoticed when the species of the whole world are placed side by side. It would likewise be instructive to exhibit the species of every country in juxtaposition with their nearest allies or representatives in other countries, and to show specimens of widely-distributed species from the centre and the extremes of its range. Surely if any nation can produce such an institution it ought to be England; yet hitherto we have little even pointing in this direction save the collections of "British " birds and insects, which have been multiplied both by public institutions and by private collectors, and which are the less instructive because Britain is not a definite zoological district, but merely an impoverished portion of the north-western Palearctic region. Is it too much to hope that the great Colonial Museum which looms in the future, and which by the special favour of all good powers is to be placed on the Thames Embankment, may include a department of the kind desired?

We must now, however, take our leave of Mr. Wallace and of his truly magnificent contribution to Natural History. If we cannot pronounce the work as in all respects perfect -if we here and there entertain a doubt or desire fuller information-the cause lies not in any shortcoming on the part of the author, but in the extent and the complexity of the subject and in the limited state of our present knowledge. The plan which he has traced with so masterly a

hand will doubtless be elaborated in its details, and may perhaps here and there be somewhat modified. But we shall all feel that Alfred Russel Wallace is the architect whose designs we are carrying out.

V. ON THE LOESS OF THE RHINE AND THE DANUBE.

THE

By THOMAS Belt, F.G.S.

HE sides of the valleys of the Rhine and the Danube, as well as those of their tributaries, are covered with a yellowish grey calcareous clay up to a height of several hundred feet above the rivers. This clay is often of great depth, is unstratified, and contains land and freshwater shells scattered throughout it. It also contains the bones and the stone implements of paleolithic man, and the remains of the mammoth, the woolly rhinoceros, and other Mammalia. This clay has been named the Loess, and respecting its origin and its relation to the excavation of the great valleys there is much difference of opinion.

Sir Charles Lyell, in commencing an able summary of the facts respecting the distribution of this deposit, states that skilful geologists peculiarly well acquainted with the physical geography of Europe have styled the loess the most difficult geological problem.* It is certainly curious to contrast the ease with which some philosophers map out the world in former geological periods, showing with confidence which areas have been beneath the sea and which remained dry land, with the difficulty that is experienced in getting any idea of what was the condition of the continents during the formation of the latest deposits, after man had penetrated into Europe, and all the species of animals and plants now living had come into existence. And yet, until we understand the youngest of the geological formations, it is almost idle to speculate on the more ancient conditions of the earth's surface. Whilst, for instance, it is held by many that much of northern Europe and America was depressed below the level of the sea in post-tertiary times, and rose

* Antiquity of Man, 4th edition, p. 372.