e north temperate zone.

[192] Sir Joseph Hooker informs me that he considers these identifications
worthless, and Mr. Bentham has also written very strongly against the value
of similar identifications by Heer and Unger. Giving due weight to the
opinions of these eminent botanists we must admit that Australian genera
have not yet been _demonstrated_ to have existed in Europe during the
Tertiary period; but, on the other hand, the evidence that they did so
appears to have some weight, on account of the improbability that the
numerous resemblances to Australian plants which have been noticed by
different observers should _all_ be illusory; while the well established
fact of the former wide distribution of many tropical or now restricted
types of plants and animals, so frequently illustrated in the present
volume, removes the antecedent improbability which is supposed to attach to
such identifications. I am myself the more inclined to accept them,
because, according to the views here advocated, such migrations must have
taken place at remote as well as at recent epochs; and the preservation of
some of these types in Australia while they have become extinct in Europe,
is exactly paralleled by numerous facts in the distribution of animals
which have been already referred to in Chapter XIX., and elsewhere in this
volume, and also repeatedly in my larger work.

[193] Out of forty-two genera from the Eocene of Sheppey enumerated by Dr.
Ettingshausen in the _Geological Magazine_ for January 1880, only two or
three appear to be extinct, while there is a most extraordinary
intermixture of tropical and temperate forms--Musa, Nipa, and Victoria,
with Corylus, Prunus, Acer, &c. The rich Miocene flora of Switzerland,
described by Professor Heer, presents a still larger proportion of living
genera.

[194] The recent discovery by Lieutenant Jensen of a rich flora on rocky
peaks rising out of the continental ice of Greenland, as well as the
abundant vegetation of the highest northern latitudes, renders it possible
that even now the Antarctic continent may not be wholly destitute of
vegetation, although its climate and physical condition are far less
favourable than those of the Arctic lands. (See _Nature_, Vol. XXI. p.
345.)

[195] Dr. Hector notes the occurrence of the genus _Dammara_ in Triassic
deposits, while in the Jurassic period New Zealand possessed the genera
_Palaeozamia_, _Oleandrium_, _Alethopteris_, _Camptopteris_, _Cyca