REPORT ON THE DEEP-SEA DEPOSITS. 
19 
always to the examination of isolated crystals or fragments of minerals such as are found 
in the deep-sea deposits. There are many characters which are passed over in silence, 
though no less important than the others, but these properties are only shown when the 
minerals are cut into numerous sections in various directions, and therefore but rarely 
seen in such isolated grains. It should also be remembered that the determination is 
much more difficult because these particles are of very small dimensions, are mixed 
with a large quantity of amorphous substances, are generally decomposed and altered by 
chemical or physical agencies, and in this isolated state do not present the associations 
which are met with in crystalline rocks. Only those mineral species that are well 
defined and individualised are mentioned, and their characters given in the following 
short descriptions. When speaking of the “fiue washings” we shall indicate some 
of the principal characters of the amorphous matters which are present in the deposits, 
such as clayey matters, oxides of iron and manganese, organic substances, phosphatic 
grains, &c. 
Amphibolb. — Hornblende. — Although minerals of the amphibolic group are more or less frequent in the 
deposits it is rather difficult, except in the case of glaucophane, to distinguish the varieties owing to the 
minuteness of the grains and to their clastic nature. We have generally to deal with common or with basaltic 
hornblende. The fragments of these tv,'o varieties are generally prismatic, with a perfect cleavage of 124° 
parallel to the prism, high relief and interference colour.s, the greatest extinction angle rarely exceeding 20°. 
Common hornblende, more or less distinctly prismatic individuals, generally greenish, rarely brownish, colours of 
pleochroism green. Associated with quartz, epidote, felspar, and other debris of older crystalline rocks. In some 
cases fragments of actinolite are found as columnar or fibrous aggregates with debris of crystalline or actinolite 
schists. Basaltic hornblende, fragments of well-crystallised individuals, sometimes regularly bounded crystals 
coated with volcanic glass, well-marked cleavage, high lustre on the planes of cleavage, black by reflected and 
brown by transmitted light, strong pleochroism and absorption, small angles of extinction, vitreous inclusions, 
in some cases coating of magnetite and characteristic corrosion. 
Glaucophane . — This mineral is somewhat rare in the deposits ; it is observed in the form of small 
prismatic fragments and is distinguished by its highly-pronounced violet-blue colour, and by the angle of the 
prismatic cleavage, which is the same as for amphibole. The extinction angle on the klinopinakoid does not 
exceed 7°. Strong pleochroism : blue, bluish violet, yellowish grey. Occurs with land debris and fragments 
of mica-schists and gneissic rocks. 
Apatite. — This mineral, rarely found in the deposits, is observed in the form of hexagonal columnar 
fragments, sometimes in elongated or rounded grains. The surface is corroded and full of small cavities, 
extinction parallel to the length, colourless, or but slightly coloured, in this case pleochroic, high index of 
refraction, considerable relief. Readily soluble in acids, tested by microchemical reaction with molybdate of 
ammonium and by' sulphuric acid. These microchemical reactions were also used in the determination of 
small phosphatic concretions and of grains of the same nature. Apatite was found with fragments of older 
crystalline rocks (see chapter on phosphatic nodules). 
Calcite. — Besides the great number of the remains of organisms or skeletons formed of calcite or of 
aragonite, this mineral is often observed in the deposits bounded by the cleavage planes or as radiated or fibrous 
aggregations. These fragments or concretions of calcite are generally characterised by the twinning parallel to 
— J R, or by the cleavage parallel to R, colourless, sometimes coloured with limonite, bluish, yellowish, and 
occasionally milky or almost opaque. Small relief, between crossed nicols presents characteristic irisation, high 
interference colours, stronger absorption of the ordinary ray j is distinguished by the facility with which it i.s 
attacked by cold hydrochloric acid. Calcite of organic origin can almost always be distinguished by its form 
