REPORT ON THE DEEP-SEA DEPOSITS. 
279 
The gradual disappearance of the carbonate of lime remains from deep-sea deposits 
with increasing depth is exhibited in the following table giving the mean percentages 
of carbonate of lime in 231 samples of organic oozes, Eed Clays, and Coral Muds from 
the Challenger collections, arranged in groups of 500 fathoms : — 
14 cases under 500 
fathoms. 
average per 
cent. CaCOs, 
86-04 
7 „ 
from 500 to 1000 
5 ? 
33 
33 
66-86 
24 „ 
„ 1000 to 1500 
y 
33 
3 3 • 
70-87 
42 „ 
„ 1500 to 2000 
)) 
33 
33 
69-55 
00 
„ 2000 to 2500 
33 
3 3 
33 • • 
46-73 
65 „ 
„ 2500 to 3000 
33 
33 
33 • • 
17-36 
8 „ 
„ 3000 to 3500 
3 3 
33 
33 • • 
0-88 
2 „ 
„ 3500 to 4000 
33 
3 ? 
33 • • 
0-00 
1 „ 
over 4000 
33 
35 
33 • 
trace. 
The fourteen samples under 500 fathoms are chiefly Coral Muds ; in the seven 
samples from between 500 and 1000 fathoms there are many mineral particles from 
neighbouring continents and islands. In all the depths beyond 1000 fathoms the 
carbonate of lime is almost exclusively derived from the shells of pelagic organisms 
that have fallen to the bottom from the surface waters, and it wiU be observed that in 
all the greatest depths of the ocean all of these pelagic calcareous shells have dis- 
appeared from the deposits. 
Many years ago Sorby ^ called attention to the importance of observing the form in 
which carbonate of lime is built up in animal structures : whether the shells be com- 
posed of aragonite or of calcite. According to him some shells are found to be com- 
posed wholly of calcite, while others are composed of aragonite or of layers of calcite 
and aragonite.^ The prismatic aragonite is much less stable than calcite, and consequently 
much more soluble. It has been stated by geologists that in some geological formations 
the aragonite shells were completely removed from the rock while the calcite shells were 
preserved. Some observers ^ have attempted to apply the same reasoning to the dis- 
appearance of the calcareous shells from the deeper deposits of the oceanic basins, it 
being held that the aragonite shells, or the aragonite portions of shells, have been removed 
in solution while the calcite shells, or the calcite portions of shells, are preserved in the 
deposits. It does not appear to us that any suflicient explanation of the facts to which 
we have just referred can be found in this direction. It is exceedingly difficult to 
determine by optical means whether or not any of these pelagic and microscopic shells 
are aragonite, and it is equally difficult to apply the specific gravity test with accuracy. 
1 Sorby, Presidential Address to the Geological Society, February 1879. 
2 See also F. Leydolt, Sitzungsb. d. k. Akad. Wiss. Wien, Bd. xix. pp. 10-32, 1856 ; G. Rose, Abhandl. d. k. Akad. 
Wise. Berlin, 1858 (Phys. KL), pp. 63-111. 
3 Th. Fuchs, Sitzb. d. k. AJcad. Wiss. Wien, Bd. Ixxvi. pp. 329-334, 1877 ; Neues Jahrbuch fur Min. etc., Jahrg. 
1882, Bd. ii. pp. 487-584. 
