CENTRAL HEAT OF THE EARTH. 421 
for example, are found in their fossil state in all latitudes, 
and even in the centre of the frozen regions of Siberia. 
In the primitive world, these northern regions enjoyed 
then, in winter, a temperature at least equal to that 
which is experienced in the present day under the paral- 
lels where the great palms commence to appear: at 
Tobolsk, the inhabitants enjoyed the climate of Alicante 
or Algiers ! 
We shall deduce new proofs of this mysterious result 
from an attentive examination of the size of plants. 
There exist, in the present day, willow grass or marshy 
rushes, ferns, and lycopodes, in Europe as well as in the 
tropical regions; but they are not met with in large di- 
mensions, except in warm countries. ‘Thus, to compare 
together the dimensions of the same plants is, in reality, 
to compare, in respect to temperature, the regions where 
they are produced. Well, place beside the fossil plants 
of our coal mines, I will not say the analogous plants of 
Europe, but those which grow in the countries of South 
America, and which are most celebrated for the richness 
of their vegetation, and you will find the former to be of 
incomparably greater dimensions than the latter. 
The fossil flora of France, England, Germany, and 
Scandinavia offer, for example, ferns ninety feet high, 
the stalks being six feet in diameter, or eighteen feet in 
circumference. 
The lycopodes which, in the present day, whether in 
cold or temperate climates, are creeping-plants rising 
hardly to the height of a decimétre above the soil ; which 
even at the equator, under the most favourable circum- 
stances, do not attain a height of more than one métre, 
had in Europe, in the primitive world, an altitude of 
twenty-five metres. 
