196 
ISLAND LIFE. 
[part I. 
persistent cold epochs when the excentricity was as low as it 
is now or lower, for that would imply that the duration of cold 
conditions was greater than that of warm. Why then should 
the fauna and flora of the cold epochs never be preserved ? 
Mollusca and many other forms of life are abundant in the 
Arctic seas, and there is often a luxuriant dwarf woody vegeta- 
tion on the land, yet in no one case has a single example of 
such a fauna or flora been discovered of a date anterior to the 
last glacial epoch. And this argument is very much strength- 
ened when we remember that an exactly analogous series of 
facts is found over all the temperate zones. Everywhere we 
have abundant floras and faunas indicating warmer conditions 
than such as now prevail, but never in a single instance one 
which as clearly indicates colder conditions. The fact that 
drift with Arctic shells was deposited during the last glacial 
epoch, as well as gravels and crag with the remains of arctic 
animals and plants, shows us that there is nothing to prevent 
such deposits being formed in cold as well as in warm periods ; 
and it is quite impossible to believe that in every place and at 
all epochs all records of the former have been destroyed, while 
in a considerable number of instances those of the latter have 
been preserved. When to this uniform testimony of the palaeon- 
tological evidence we add the equally uniform absence of any 
indication of those ice-borne rocks, boulders, and drift, which 
are the constant and necessary accompaniment of every period 
of glaciation, and which must inevitably pervade all the marine 
deposits formed over a wide area so long as the state of glacia- 
tion continues, we are driven to the conclusion that the last 
glacial epoch of the northern hemisphere was exceptional, 
and was not preceded by numerous similar glacial epochs 
throughout Tertiary and Secondary time. 
But although glacial epochs (with the one or two excep- 
tions already referred to) were certainly absent, considerable 
changes of climate may have frequently occurred, and these 
would lead to important changes in the organic world. We can 
hardly doubt that some such change occurred between the Lower 
and Upper Cretaceous periods, the floras of which exhibit such 
an extraordinary contrast in general character. We have also 
