510 
Proceedings of the Royal Society 
barrier and fringing reefs facing continents we may bave a great 
variety of rocks and minerals. Beyond a depth of 1000 fathoms 
off coral islands the debris of the reefs begins to diminish, and the 
remains of pelagic organisms to increase ; the deposit becomes more 
argillaceous, of a reddish or rose colour, and gradually passes into a 
Globigerina ooze or a red clay. Coral Sands contain much less 
amorj^hons matter than coral muds, but in other respects they are 
similar, the sands being usually found nearer the reefs and in 
shallower water than the muds, except inside lagoons. In some 
regions the remains of calcareous algse predominate, and in these 
cases the name coralline mud or sand is employed to point out the 
distinction. 
Such is a rapid view of the deposits found in the deeper waters 
of the littoral zones, where the debris from the neighbouring 
land plays the most important part in the formation of muds and 
sands. When, however, we pass heyond a distance of about 
200 miles from land, we find that the deposits are characterised by 
the great abundance of fragmentary volcanic materials which have 
usually undergone great alteration, and by the enormous abundance 
of the shells and skeletons of minute pelagic organisms which have 
fallen to the bottom from the surface waters. These true deep-sea 
deposits may be divided into those in which the organic elements 
predominate, and those in which the mineral constituents play the 
chief part. We commence with the former. 
Globigerina Ooze. — We designate by this name all those truly 
pelagic deposits containing over 40 per cent, of carbonate of lime, 
which consists principally of the dead shells of pelagic Foraminifera — ■ 
Globigerina^ Orbidina, Pulviimlma, Pidlenia, SphcBroidinay &c. 
In some localities this deposit contains 95 per cent, of carbonate 
of lime. The colour is milky white, yellow, brown, or rose, the 
varieties of colour depending principally on the relative abundance 
in the deposit of the oxides of iron and manganese. This ooze is 
fine grained ; in the tropics some of the Foraminifera shells are 
macroscopic. When dried it is pulverulent. Analyses show that 
the sediment contains, in addition to carbonate of lime, j^hosphate 
and sulphate of lime, carbonate of magnesia, oxides of iron and man- 
ganese, and argillaceous matters. The residue is of a reddish-brown 
