GEOLOGY OF BOTTOM OF SEAS—DE LAUNAY. 341 
of it, but the name globigerina ooze is reserved for cases where the 
proportion exceeds 30 per cent. These globigerina oozes contain 
a little less than 2 per cent of siliceous organisms and a certain 
proportion of clay, which tends to be increased by the dissolving 
of limestone in diagenesis. Finally the globigerma ooze becomes a 
red clay. 
A map of the marine beds reveals the predominant réle of these 
globigerina oozes, except in the Pacific, where the latest explora- 
tions of the Albatross have, however, found some zones of consid- 
erable extent. More locally at a maximum depth of 3,000 meters 
some pteropod oozes are found, which are indicated on the map of 
the Atlantic. 
Let us pass now to the siliceous oozes. Here the origin of the 
silica is the clay which exists in fine suspension down into the extreme 
depths. It is supposed that the chemical medium is furnished by 
decomposing organic matter which reduces the sulphates to alkaline 
sulphides, after which the latter in their turn act on the clay. Ex- 
periments by Murray and Irvine have shown that in order to sus- 
tain life in diatoms in a liquid there must be a supply of pulverized 
clay. 
Now, the quantity of clayey material remaining in suspension 
increases in proportion as the temperature of the water decreases. 
This is without doubt one of the reasons why siliceous diatoms are 
particularly abundant in cold water. But this phenomenon is 
complex and the observation should not be generalized upon. 
The siliceous organisms comprise sponges, diatoms, and radiola- 
rians. Only the last form in the sea distinctive deposits. The others 
remain in a state of balance in the calcareous deposits. Sponges 
have a very extended area of dispersion because their embryos swim 
freely and their spicules are found in the most diverse strata. They 
are quickly dissolved and help to keep the silica in motion. Di- 
atoms, siliceous alge, live in waters of weak salinity, such as estu- 
aries. Immense floating banks of them are met with in the Atlantic 
many kilometers long and several meters deep. They are developed 
like calcareous algz in the upper layers of water, where they serve as 
food for numerous marine animals, after which their débris falls to 
the bottom. An extensive train of them is found in the Antarctic 
Ocean, another to the south of Bering Strait. And, furthermore, 
contrary to what was claimed some years ago, the Albatross observed 
them in a warm region in latitude 12° south on the coast of South 
America. The radiolarians live chiefly in warm and relatively quiet 
waters. Their deposits form an equatorial track across the Pacific 
from the Gulf of Mexico toward Australia, then between Australia 
and Java. In places in the Pacific the siliceous organisms dominate 
