66 Prof. O. Heer on the Miocene Flora 
beautiful and varied fossil plants which fill the rocks of Atane- 
verdlak in Greenland, will be convinced that these plants can- 
not have come from a great distance. As to the fossil plants 
of Spitzbergen, it is very evident that they were not brought 
by marine currents, as we find them in freshwater deposits. 
It appears certain, therefore, that at the Miocene epoch the 
temperature of the polar regions was much higher than in 
our day; and we are naturally led to inquire what are the 
causes which may have brought about such a change. We 
cannot admit the supposition of a displacement of the poles, 
even regarding it in the same way as Mr. Evans, who has re- 
cently maintained this theory. Indeed it is a certain fact that 
we remark the same phenomena all round the terrestrial globe, 
not only in the polar zone, but also under southern latitudes. 
No direct observation seems to us to confirm this hypothesis. 
We regard as much more important the theory according to 
which climatic modifications would coincide with modifica- 
tions in the distribution of the seas and continents upon the 
surface of the globe. At present the extent of the seas is 
twice and a half that of the solid earth, and the continents are 
arranged in much more considerable masses in the northern 
hemisphere, and especially beyond the tropic. This condition 
is not normal. If, instead of so unequal a distribution, the 
lands and seas were equally distributed in all the zones, the 
temperate and glacial zones would enjoy a climate warmer 
than at present. Nevertheless, even supposing the most 
favourable distribution, we should not succeed in producing, 
between 70° and 79° N. latitude, a temperature sufficient for 
the development of a flora like that of which the existence 
in these regions during the Miocene period has just been in- 
dicated. Suppose all the continents united in the neighbour- 
hood of the equator, and only a few islands left in the northern 
revions,—these would enjoy the highest mean temperature to 
which they could attain, their winters would be compara- 
tively very mild, and yet the heat of the sun could not be suf- 
ficient between 70° and 80° N. lat. to allow of the development 
of a vegetation so rich as that of which we find the traces. 
Now it is certain that in the Miocene period there was a great 
extent of solid land in the temperate zone, and even in the 
polar regions, as is proved to us by the extension of several 
species of the Miocene flora, which we can follow from the 
Mackenzie to Spitzbergen. 
The explanation of the climatic changes which the study of 
fossils reveals to us, has been sought in the fact that the 
gradual cooling of the mass of the globe must necessarily pro- 
duce a gradual diminution of temperature. This cause may 
certainly have acted in the most ancient periods; but the Mio- 
