8 
most part identical, but also that of the few fossil plants 
from Baffin's Bay, New Holland, and Hindoostan (from the 
northern, the southern, and the torrid zones), the chief are 
genera belonging to the same natural groups with those which 
predominate in the coal formations of central Europe ; and 
this uniformity of vegetation is one strong evidence of uni- 
formity of temperature, as well as of other physical conditions. 
With respect to the Ferns, however, which of all fossil 
plants can alone be referred with certainty to their proper 
place in the vegetable kingdom, and in a recent state have, 
of all plants, the widest geographical distribution, a glance, 
for a few moments, at the range of a few of the existing 
species, may throw some light on the fact before alluded 
to, — of the identity of species in the fossil floras of Europe, 
America, and Australia, and which appear less extraor- 
dinary if we observe the large proportion of ferns in the 
ancient vegetation, and their distribution at the present day. 
Thus of forty-two ferns found in the North of Italy, 
thirty-four are also British. Iceland has fourteen ferns, all 
of which are British, and all, but one, found in Italy. Of 
twenty-six ferns enumerated as natives of Greece, twenty- 
one are British, and eight common to Greece and Iceland. 
One-third of the ferns of Madeira — twelve out of thirty-six, 
are British; two species, Polypodium vulgare and Cystopteris 
fragilis, are common to Madeira and Iceland, a greater 
latitude than any fossil fern has yet been found to possess. 
Sixteen out of twenty-eight ferns of the Azores are British. 
When we cross the Atlantic a greater difference is observ- 
able. Out of sixty-nine ferns of North America only thirteen 
are European species. It is also assumed that within the 
tropics ferns have a very wide range, as, for instance, from 
the West Indies to Rio de Janeiro. Still, however, if we 
take the uniformity of vegetation as testified by the ancient 
flora extending over so large an area as from Scotland to 
