DEPOSITION IN THE SEA 259 
Red Clay. In the deeper parts of the ocean, even this slowly 
accumulating deposit is absent; for at these great depths, the 
ocean water is able to dissolve the carbonate of lime of the shells 
as they settle. Therefore the only portion which reaches the 
bottom is the minute remnant of insoluble impurities. To this 
is added fragments of pumice from volcanic eruptions, for this 
rock material is falling over the surface of every ocean, and 
sinking to the bot- 
tom whenever it 
decays or becomes 
water-logged. 
This very fine- 
grained clay accu- 
mulation is colored 
red by iron com- 
pounds from the 
volcanic ash, and 
from particles of 
meteorites which 
have burned in the 
air and dropped into 
the water. Soslowly 
are these red clay 
deposits gathering, 
that fragments of meteorites have been found even in the few 
places where dredgings have been made. Red clay rocks are not 
known to exist among the strata that form the continents, and so 
it seems fair to conclude that these have never been submerged 
in really deep water. This interesting red clay is estimated to 
cover an area of ocean bottom equal to fully 50,000,000 square 
miles. 
Fie. 147. 
Photograph of a microscopic enlargement of chalk 
from Iowa, showing shells of Globigerina. 
