Notices of Books . 
39i 
1876.] 
its authors, and not less on the Government which so liberally 
places it in the hands of learned societies throughout the world. 
In addition to illustrations inserted in the text, there are fifty- 
three large lithographed plates, most carefully executed and 
well explained. Such work as this volume represents is abso- 
lutely necessary for the progress both of geology and zoology. 
At the same time it is evidently beyond the means of private 
individuals. We can only therefore wish that the noble example 
set by the Government of the United States may be followed 
elsewhere. Incidentally we may notice that the measurements 
of the various fossil remains investigated are given on the metric 
system. 
The authors infer from their researches that the distinCt 
faunal areas which the earth now presents — the more prominent 
among which are those respectively of Australia, of South 
America, and of the temperate regions of the northern hemi- 
sphere — have always prevailed, so far, at least, as the extinCt 
Mammalia are concerned. The writers ask — “ Was the suc- 
cession of interruptions of life universal over the globe, and do 
these trenchant lines justify the old assumption of repeated 
destructions and recreations of animal life ? The former ques- 
tion has already been answered in the negative by the explana- 
tion of the characters of the existing faunae of the southern 
hemisphere, where ancient types still remain in considerable 
numbers. Moreover, some of the later periods, both of North 
America and Europe, are characterised by a large predominance 
of forms of the corresponding southern continent. It is, indeed, 
evident that migration from the one continent to the other has 
taken place, and is amply sufficient to account for the abrupt 
changes in the life of each without necessitating the intervention 
of creative aCts. If glacial periods be dependent on cosmic 
movements, the increased obliquity of the earth’s axis to the 
sun at periods 25,000 years apart would cause a corresponding 
alternation of cold periods in the opposite hemispheres. This 
is well known as a most potent cause of migration and extinction, 
and the known relations of the faunae would thus result from a 
greater or less alternate invasion of one hemisphere by the life 
of the other.” 
The distinCt terrestrial faunae within these great periods are 
referred to the “ alternate presence and absence of water-areas 
adapted for the preservation of animal remains,” — a variation 
due to the slow vertical oscillations of the earth’s crust. 
Hence it appears that the authors do not find any evidence 
favourable to the vicious principle of omnia per a re- 
actionary doCtrine whose rehabilitation is in some quarters so 
earnestly attempted. 
