266 On the Old and New World. 
tainly to affirm that the number of analogous races is extremely 
restricted, but that many exist, (principally among animals), which 
we cannot help regarding as identical with our own. It appears to 
be the same with vegetables. 
Nore 20. Active volcanoes are true safety-valves for the adja- 
cent regions. It is the same with thermal waters. If the opening 
of a volcano has been closed, and the communication with the at- 
mosphere interrupted, the neighbouring countries are threatened with 
shocks. We may well suppose that there exist, in the interior of 
the earth, a source of electro-magnetic currents, polar auroree, and 
irregular movements which disturb its surface. 
Norte 21. Not only do the great phenomena which took place 
during geological times still occur in the present day, but it is the 
same with those which, by being on a smaller scale, are less fitted 
to arrest our attention. Thus the fall of stones or meteoric masses 
is constantly perpetuated on the surface of the globe; they are dis- 
covered as well in the interior strata as on the surface of the earth. 
The phenomenon of aerolites is not peculiar to our epoch, since fossil 
ones exist; it is continued from geological times to our own day. 
On the other hand, the petrifaction of organized bodies is not con- 
fined to times anterior to our own epoch; it is taking place to-day 
both in fresh water and in salt. We have ourselves proved that 
vegetables petrify in the former, just as the remains of molluses or 
shells do in the latter. If we are not certain that the same thing 
takes place with bones, it is probably because we have not been 
placed in circumstances favourable to the discovery of them in that 
state. It is not at least to be supposed, that wood, grains, shells, 
and the tubes of the annelides, should be capable of passing into a 
stony state, and that it should not be the same with osseous remains 
charged with calcareous matter, and already in a solid condition. In 
consequence of this peculiarity in a great number of organic remains, 
of being capable of being replaced by an inorganic matter more solid 
than that of which they were first composed, sandstones and beds 
of shells are forming every day on the beaches of existing seas ; 
these beds have the closest analogy to the shell-banks of the tertiary 
epoch, 
