GEOLOGY OF BOTTOM OF SEAS—DE LAUNAY. a00 
crust have come in geologic history those oscillations of the seas of 
which I was speaking a while ago. 
And we shall end by examining how an ancient sea could become 
dry land, how an ancient continent could become sea. This will 
lead us definitely to discuss the bottom of the sea as a continent and 
to attempt that method of mapping which sums up the entire geol- 
- ogy of a country, the establishment of submarine geologic charts. 
You see that this is a very comprehensive program, and one that 
would fit an entire book rather than a single lecture. If I were to 
give it the development that it deserves, I should be obliged to appear 
before you many times. I shall be content, therefore, in this lecture 
to indicate its most characteristic outlines. 
At this poimt I must confess to you, furthermore, that my task 
consequently, if not easy, will at least be abridged. The geology of 
the bottom of the seas, with which I shall try to entertain you, is 
still very poorly known to us. Interrogation points are presented 
on, all sides and very few of them have been answered. We should 
not complain too much about this. No doubt what I shall have to 
say to you here this evening will lack interest. But what is not 
known remains to be learned. That is the harvest of the future. It 
is the grain which is springing up. It is the almost unexplored field 
where one may hope some day to find the key to problems that 
terrestrial geology elsewhere proposes to us. The search that arouses 
the fever of discovery is always joyous, when in the great palace of 
truth, here flooded with light and surrounded by the throng, there 
already lighted by pale rays and accessible to the rare passers, it 
percetves some corners now shrouded in dense darkness where in 
imagination it hopes may presently shine forth marvellous invisible 
treasures which hardly yet attract the covetous. 
Although we know little of the geology of the bottom of the seas, 
it is almost enough to define it, to comprehend it. Oceanic geology 
proposes to us, as I have said, for parts of the earth at present again 
covered by the waters, the same problems that terrestrial geology 
seeks to solve in regions now emerged. It likewise seeks to know, 
from one point to another, what the accumulation of sediments is 
which have been deposited in successive periods of a very old history 
or which are still being deposited there, to what movements these 
strata have been subjected, what eruptive rocks have traversed them. 
Whether located in the depths of the oceans or placed on our con- 
tinents, the point of view, from this fact alone, is not different. Now 
we already often have much difficulty in recognizing the complete 
and exact geologic history of a place on our continents, the very 
ones most readily accessible, like Paris, the most furrowed by cut- 
tings and perforated by borings. How much more so when it is 
necessary to work under water several thousands of meters deep? 
