GEOLOGY OF BOTTOM OF SEAS—DE LAUNAY. 333 
ing continents, but even oceans like the Atlantic or the Indian Ocean, 
where we so naturally picture ancient continents having united 
Brazil and South Africa, or Madagascar and India, to be later 
broken up by sinking. These sinkings must have been not merely the 
counter-equivalent of folded ranges localized along the length of old 
geosynclines; it is entirely probable that they had as a consequence 
or as a corollary the removal, at least relative, of other deep ter- 
restrial cavities, left so by the passing out of the waters. In the 
Pacific likewise the evident dissolving of certain Tertiary deposits, 
notably in some of the coral islands, proves that the land has moved 
vertically in a recent epoch.! 
Oceanography will some day tell us exactly what there is in these 
hypotheses. Suppose, in fact, that a marine basin had been con- 
stantly filled by the sea since its origin (which with few exceptions is 
entirely possible). We then ought at this point to meet with a 
sedimentary series complete, without break, extending from the 
pre-Cambrian to the Quaternary. A sounding deep enough, travers- 
ing this series, would give us the ideal geologic section, the integral 
section, which would render insignificant the finest sections fur- 
nished by terrestrial escarpments (such as the Colorado Canyon), 
on condition, which is uncertain, that the parts of the formation not 
very deep might not have been entirely despoiled of their organisms 
and reduced to a clayey residue by diagenesis. Even if the section 
presented some gaps its study would give us information, in a pre- 
cise and directly experimental way, on one of the most obscure 
problems in the history of the globe. 
I repeat then, because I know that my opinion on this point is 
not accepted by all geologists, that as a rule, save in exceptional cases, 
it does not appear to me necessary to establish a fundamental differ- 
ence, a permanent difference, between the regions to-day occupied by 
the seas and those occupied by terra firma. I do not believe that 
in their entirety, with some possible exceptions to which we shall 
return, the present oceans, since the beginning of geologic history, 
have had their sites marked out in advance to be continuously occu- 
pied as heretofore by the waters. The difference between the seas 
and the continents, which forms the most characteristic feature of 
our physical geography, is to my eyes only a momentary stage in a 
continuous evolution through all past ages and probably destined to 
be continued through all ages yet to come. 
When one studies geology, the first notion with which it is neces- 
sary to familiarize oneself is that of the instability of the seas. One 
must picture to himself that over the present site of all our conti- 
nents, almost without exception, the seas have passed during an 
1 Robert Douvillé gave in La Nature, 1911, pp. 401-405, a good résumé of the history of the Pacific. 
