

FOSSILS 99 
of a milder and more equable climate than now characterises 
Northern France. And the same is the case with the Polar 
willow, the evidence supplied by it being fortified by that 
of other high northern plants, and by the relics of such animals 
as lemming, arctic fox, etc. 
Great caution must be exercised in deducing climatic 
conditions from the occurrence of éxtinct forms of life. For 
these, even when they very closely resemble living types, 
need not have existed under similar conditions. For example, 
so long as the mammoth and woolly rhinoceros were only 
known from their skeletal remains, they were generally 
supposed to have existed under the same climatic conditions 
as their living representatives. We know now, however, that 
each was provided with a thick woolly and hairy covering, 
and was capable, therefore, of withstanding the rigours of a 
northern winter. 
In dealing with fossils consisting largely of extinct species, 
it is the general facies of a flora and fauna, and not individual 
forms, that are to be specially considered. For example, the 
London Clay (Eocene) has yielded a large number of types 
having a tropical or subtropical aspect. Amongst the plants 
are forms of sarsaparilla, aloe, amomum, fan-palms, fig, liquid- 
ambar, magnolia, eucalyptus, cinnamon, various proteaceous 
plants, etc.; while the animals include turtles, tortoises, 
crocodiles, tapir-like pachyderms, and certain birds with 
affinities to living tropical types. Associated with these are 
many forms of molluscan life which have their nearest living 
representatives in warm latitudes, such as cones, cowries, 
volutes, nautilus, etc, together with sword-fish, saw-fish, 
sharks, and rays. All this is good evidence that a warm 
climate prevailed during the deposition of the London Clay. 
The land was clothed with a tropical or subtropical vegetation, 
while analogous types of animal-life haunted the rivers and 
flourished in the sea of the period. 
In the older geological systems we may say that all the 
species and nearly all the genera are extinct, so that any 
generai resemblance which an assemblage of Palzozoic fossils 
may have to those of some particular groups of living plants 
and animals may have no climatic significance whatsoever. 
We may feel sure, indeed, that the abundant flora of the 
