June 29, 1876] 



NATURE 



187 



us, " that we are now in an altogether exceptional period 

 of the earth's history," some idea of which it is very neces- 

 sary to realise. " We live in an impoverished world, from 

 which all the hugest and fiercest and strangest forms 

 have recently disappeared." The cause of this great 

 change over such a large part of the world's surface was, 

 in Mr. Wallace's opinion, the "glacial epoch," which, 

 according to Mr. Belt's theory, heaped up most of the 

 water in the earth in mountains of ice round the two poles 

 and left the great ocean-beds comparatively dry. This, 

 we are told, " must have acted in various ways to have 

 produced alterations of the levels of the ocean as well as 

 vast local flows, which would have combined with the 

 excessive cold to destroy animal life." We are not sure 

 that this is a very satisfactory explanation of the simul- 

 taneous disappearance of the great Irish Elk from Europe 



and the Megaiheriuvi from South America, but it is at all 

 events some explanation of an obscure point, and deserves 

 careful consideration. So also do those few cases in 

 which geological evidence is already sufficient to give us 

 indications of the original birth-place of some of the mam- 

 malian types, and of the mode in which has come about 

 their present state of distribution. 



The third section of Mr. Wallace's great work, which 

 we now enter upon, is, in fact, the most important of the 

 whole, and that to which the previous chapters may be 

 regarded purely as introductorj'. Having shown us what 

 the six great divisions of the earth's land-surface, zoo- 

 logically considered, are, and how it may have come to 

 pass that they are what they are, Mr. Wallace takes them 

 one after the other in order, and gives us a separate 

 memoir upon each of them, and their special zoological 



Fig. 3. — A Brazilian Foreit, with characteristic Mammalia. 



characteristics. After a description of their territorial 

 outlines, illustrated by hypsometrical maps in which the 

 boundaries of the sub-regions are likewise indicated, 

 general remarks are given upon their leading zoological 

 features. The chief forms of mammals, birds, reptiles, 

 batrachians, fishes, butterflies, beetles, and land-shells, 

 which characterise them are pointed out. The Sub- 

 regions into which they are divisible are then taken up 

 and treated in greater detail, and the leading authorities 

 from whose labours the necessary facts have become 

 known to us are cited. At the end of each memoir 

 " tables of distribution " are added, in which are given — 

 first, a list of the families of the selected groups of 

 animals represented within the Region, with an indication 

 of their range, if any, beyond the Region, and secondly, 

 a similar list of the genera of the terrestrial mammals 



and birds, with an indication of their ranges both within 

 and beyond the Region. Three or four plates, drawn by 

 the late Mr. J. B. Zwecker, accompany each memoir. 



These are intended to illustrate the physical aspect and 

 zoological character of some well-marked division of the 

 region, and as only such species are figured as " do actu- 

 ally occur together in a state of nature," the scenes repre- 

 sented are " at all events not altogether impossible ones," 

 which is more than many of our artistic friends can say of 

 their productions ! While we could have wished that Mr. 

 Zwecker had resorted in some cases to the Zoological 

 Society's Gardens rather than to previously published 

 figures for the models of some of his animals, we must 

 acknowledge generally the truthfulness of these illus- 

 trations and the faithful manner in which they have been 

 executed. At home alike in the tropics of the Oriental 



