88 THE AMERICAN NATURALIST. [Vor. XXXV. 
In the introductory chapter Dr. Scharff, starting out from the 
present fauna of Great Britain and Ireland, demonstrates its 
heterogeneous composition, embracing, as it does, animals, the 
affinities or geological history of which point to their southern, 
northern, or eastern origin, and shows that in all probability the 
southern forms must have extended northward from the conti- 
nent long ages ago, while the others arrived comparatively 
recently. He then discusses the means of dispersal possessed 
by the various animals, especially *the occasional means," as 
Darwin called them, and ventures to think that both Darwin 
and Wallace have somewhat overestimated its significance, and 
he reaches the conclusion that five per cent would be a high 
estimate for the animals which have reached British soil by 
accidental means. This proportion he regards as insignificant, 
in fact as utterly negligible. 
In the second chapter, which is headed * Preliminary Con- 
siderations," Dr. Scharff endeavors to show how to determine 
approximately the original home of an animal so as to be able 
to study the component elements of the European fauna. As 
one of the results he announces that what was formerly be- 
lieved to have been one great northern invasion now resolves 
itself into two distinct ones — the Siberian and the Arctic. 
An examination of the present distribution of mammals, snails, 
and earthworms shows that the British Islands have been 
connected with one another and with the continent; Spain 
with Morocco across the Straits of Gibraltar; Greece with 
Asia Minor, and so forth. The British fauna forms the key 
to the solution of the wider problem of that of Europe, five 
elements being recognizable, of which the Lusitanian is the 
oldest and the Siberian the most recent. A discussion of the 
climate of Europe during the glacial period follows, in which 
Dr. Scharff tries to maintain that so far from being of an Arctic 
nature the climate was mild, possibly even milder than at pres- 
ent, to which result he is mainly led by a contemplation of the 
striking and most remarkable mingling of a northern and a 
southern fauna during the Ice Age. An extensive glaciation, 
as advocated by modern geologists, is consequently denied and 
evidence brought forward to demonstrate the marine origin 
