1898 - 99 .] Soundings obtained by s.s. ‘ Britannia . 5 423 
rather casts of organisms) are of a dull brownish or greyish 
colour, and are composed of crystalline carbonate of lime 
(see note below). 
Residue (10%), 
Minerals (1%), a few small particles of augite and glass. 
Siliceous Organisms (1%), Sponge spicules, imperfect casts in 
a clayey matter. 
Fine Washings (8%), amorphous clayey matter, etc. 
In this and the three neighbouring deposits (254 to 290 fathoms) 
casts of the calcareous organisms in carbonate of lime occurred. 
Such a deposition was observed in the deposit obtained by the 
‘ Challenger ’ off Raine Island, Torres Strait (155 fathoms), and 
is thus described in the Challenger Report on Deep-Sea Deposits 
(pp. 169-170) 
“ If some of the Foraminifera be treated with dilute acid, the 
action stopped after it has continued for some time, and the sub- 
stance dried and examined by reflected light, a number of casts of 
the organisms are seen in carbonate of lime looking quite like milky 
quartz. If, however, the action be continued, it is seen that they 
are composed of carbonate of lime as they entirely disappear, 
leaving a small residue of a reddish colour, or very areolar casts of 
the shells in the same red substance. Examined in thin sections, 
it is observed that the shells are filled with a red, yellowish, or 
greenish matter, frequently extending into the foramina. The 
shell is at once distinguished from the cast by its structure, trans- 
parency, and optical properties. It is sometimes observed that two 
or three shells or fragments are cemented by the same red sub- 
stance forming the casts. This substance, when sufficiently trans- 
parent, appears of a yellowish red colour, and gives sometimes 
aggregate polarisation, but is never extinguished between crossed 
nicols. Often the casts inclose small mineral particles. With 
very high powers it is seen that the structure of the grey carbonate 
of lime casts is granular, and between crossed nicols it is evident 
that the grains are crystalline. This is one of the few instances in 
which it has been possible to point out the deposition of carbonate 
of lime in the shells forming deposits, and it evidently took place 
in the deeper layers.” 
