NARRATIVE OF THE CRUISE. 
531 
By treating this deposit with dilute acid, casts of the Foraminifera shells arc obtained, 
the majority of which are of a brick red colour, although a few are of a yellowish, or 
even greenish, tinge. They are not so compact or well-marked in outline as the white and 
pale straw-coloured casts usually met with in glauconitic muds, and have very frequently 
a porous aspect, from the solution of the carbonate of lime being, in many instances, 
associated with the red material forming the casts. If some of the Foraminifera be treated 
with dilute acid, and the action stopped after it has continued for some time, and the 
substance dried and examined by reflected light, a number of casts of the organisms arc 
seen in carbonate of lime looking quite like milky quartz. If, however, the action be 
continued, it is seen that they are composed of lime as they quite disappear, leaving a 
small residue of a reddish colour, or very areolar casts of the shells in the same red sub- 
stance. 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 
m 
once distinguished from the cast by its structure, transparency, and optical properties, 
it is sometimes observed that two or three shells or fragments are cemented by the same 
red substance forming the casts. This substance when sufficiently transparent appears of 
a yellowish red colour, and gives sometimes aggregate polarisation, but is never extin- 
guished between crossed Nicols. Often the casts enclose small mineral particles. Seen 
by transmitted light, there is a great difference between the calcareous casts and the 
carbonate of lime constituting the shells themselves. These casts are but slightly 
transparent, greyish coloured, or almost opaque, the opacity being due to infinitesimal 
foreign particles which remain as a red residue after treatment with dilute hydrochloric 
acid. With very high powers it is seen that the structure of the grey calcareous casts 
is granular, and between crossed Nicols it is evident that the grains are crystalline. 
An analysis of the red coloured casts above described, obtained by treating the deposit 
with very dilute acid, was made by Dr. Sipocz ; and, although the analysis shows that 
they are composed of a hydrated silicate containing all the constituents of typical 
glauconite (iron, alumina, magnesia, and alkalies), yet the various percentages, especially 
that of silica, differ so considerably from the mean numbers obtained for glauconite, that 
the substance cannot be grouped with that mineral species. Perhaps these casts are in 
the process of becoming true glauconite. The large percentage of ferric oxide (39 to 93), 
which is in the form of hydrate, gives the red-brown colour to the casts. 
Paine Island to Cafe Yoke. 
At 1.30 p.m. Paine Island beacon bore N. 52° E., and the extremities of the Great 
Detached Reef S. 81° E. and S. 63° E. From here the ship was steered S.W. \ W. 
(under sail) towards the Ashmore Banks, which were sighted at 3.30 p.m., Hardy Island 
being seen shortly afterwards. Crossing the edge of the barrier, the 5 and 6 fathom 
