GEOLOGY OF BOTTOM OF SEAS—DE LAUNAY. 345 
the greater part of our sediments, as it is in the state of apatite in 
most of our rocks, is condensed in exceptional quantities in certain 
deposits which appear in a general way, as M. Cayeux observed in 
1897, to correspond to some disturbances of equilibrium causing an 
advance, or more rarely a withdrawal of the sea; a phenomenon in 
which it is probable that numerous living things were killed by 
changes of temperature resulting from a modification in the cur- 
rents, and consequently are accumulated at the bottom of the sea. 
Phosphate, which existed at first in solution in sea water, has passed 
through the medium of organisms; and its greater or less abundance 
is in accord with that of these organisms themselves, save that they 
later have undergone some more or less pronounced concentrations: 
in the sea itself by diagenesis or, after emergence, by metasomatosis.! 
This is the general theory that oceanography demonstrates for us. 
The Challenger expedition has already brought up from the depths 
rather numerous phosphatic concentrations. These concretions were 
encountered especially on what is called Agulhas Bank to the south 
of Cape of Good Hope, where the German expeditions in the Gazelle 
and the Valdivia again found them later, then on the east coast of 
Japan, at the junction of the warm Kuroshimo with the cold current 
of the Bering Sea, on the Atlantic coast of North America, in the 
straits of Florida, etc. The corresponding depths of water do not 
exceed 1,000 meters and are often less than 200. It may follow 
from this, that in the greater depths the precipitated phosphate of 
organisms is dissolved before reaching the bottom. 
When on a general map of the oceans you mark these localities 
of phosphatic concretions you note that they are specially present at 
the points where warm currents encountering a cold current produce 
decided variations of temperature in the surface water. You know 
how sensible marine organisms are to variations of this kind. It is 
therefore probable that organisms thus killed are accumulated at the 
bottom of the sea at the corresponding points and have there fur- 
nished the phosphate. These organisms should be especially inverte- 
brates; but there must be added some fishes, the teeth of which abound 
in certain phosphatic chalks. The constant association of carbona- 
ceous material with geologic phosphates equally proves this organic 
origin. Along the American coast, for example, a conflict is pro- 
duced between the cold Labrador current and the warm waters of the 
Gulf Stream. According to the severity of the polar winter, the cold 
current encroaches more or less on the warm stream. It was so in 
1882 when in the Atlantic Ocean off the coast of New England there 
appeared, over a width of 270 kilometers, beds of dead tilefish to a 
depth of 1.8 meters. On the other hand a general displacement of 
the seas and especially a transgression on the continents must have 
1 See, on this subject, my Traité des gites métalliféres, vol. 1, pp. 646-649, 659-661. 
