1889 - 90 .] Dr J. Murray & Mr R. Irvine on Coral Beefs. 83 
Luted in equatorial regions, but some patches of Globigerina ooze 
are to be found even within the Arctic circle in the course of the 
Gulf Stream. The table on preceding page shows the estimated 
area of the various kinds of deposits, with the average depth, and 
average percentage of carbonate of lime in each. 
One of the most remarkable facts discovered by the “ Challenger ” 
expedition is that, although the dead shells of these pelagic 
organisms are rained down on the sea bottom, and in shallower 
depths accumulate so as to form calcareous deposits of im- 
mense extent, still, in other contiguous but deeper areas, these 
shells do not accumulate on the bottom, being wholly removed 
either while falling through the water or shortly after reaching the 
ocean’s floor. The pelagic organisms are as abundant in the surface 
waters over the one area as over the other, the only apparent differ- 
ence in the conditions being one of depth. In the shallowest 
deposits of the open sea, shells representative of nearly all the 
lime-secreting surface organisms are to be found in the deposits. 
With increasing depth the more delicate ones disappear from 
the bottom till, in 1800 or 2000 fathoms, it is rare to find more 
than traces of Heteropod, Pteropod, or the more delicate pelagic 
Foraminifera, shells in the deposits, while these same delicate 
shells occasionally make up fully one-half of the carbonate of lime 
that is present in depths of 700 or 1000 fathoms. Again, in the still 
greater depths of 3000 and 4000 fathoms and deeper, the For- 
aminifera, Coccoliths, and Rhabdoliths are either wholly removed, or 
are represented only by the broken fragments of the thickest and 
most compact shells, like Pulmnulina menardii , Sphceroidina 
dehiscens, or Globigerina conglobata. This gradual decrease in the 
quantity of carbonate of lime iff the deposits with increasing depth 
is well illustrated in the following table, showing the percentage 
of lime in the samples of deep-sea deposits collected by the 
“ Challenger” towards the central parts of the ocean basins, away, 
from the immediate influence of the debris from continental land 
or volcanic islands. 
The organic oozes, including the red clays and the coral deposits, 
make up a total of 231 samples, and are arranged as follows, show- 
ing the percentage of carbonate of lime in relation to depth : — 
