254 Marcel de Serres on the Old World 
We have reminded you of the extent of seas during geo- 
logical times; you ought not therefore to be surprised that 
the examination of terrestrial strata enables us to discover 
so great a number of marine organic remains, often at con- 
siderable elevations, and very remote from the basin of 
existing seas (See Note 12). The ancient ocean has there- 
fore occupied the places where these remains appear ; as 
marine products are diffused over extensive spaces, the ocean 
must have been vastly greater than it is in the present day 
(See Note 138). 
But let not this lead you to suppose that the level of seas 
has ever reached the height of 2000 or 3000 metres above 
their present elevation. If we discover beings which have 
lived in their bosom at such elevations, they have been 
carried thither from the bottom of the ocean by upheavals ; 
this powerful cause has, in fact, greatly modified the surface 
of our planet, and is quite adequate to produce such effects 
(See Note 14). 
It is unnecessary to prove to you who now hear me, that the 
seas of geological eras occupied a greater extent than those 
of the present world. If any one, however, have any doubts 
on the subject, we should say to him, Dig into the ground 
on which this city stands, and if the marine remains you find 
there do not satisfy you, examine the beds which separate us 
from the Upper Cevennes, and you will everywhere meet with 
proofs of the long continued presence of the sea in districts 
which are now very remote from it. 
Science has not stopped here; she has been desirous to 
ascertain the depth of the marine waters which covered 
portions of the earth now become continents, and also to 
trace out the shores of the ancient ocean. She has succeeded 
in determining, by observation, these different points of fact, 
and that by a very simple means. 
She has first endeavoured to ascertain if there was not, 
for each marine species, certain zones of depth which it never 
passed. The existence of these zones once established, she 
has applied to the ancient species the laws whose constancy 
had been determined in the distribution of analogous races. 
