REPOET ON THE DEEP-SEA DEPOSITS. 
319 
associations, as well as the position with reference to distance from coasts, there is an 
excellent means of forming an opinion relative to the origin of the mineral particles 
that may be met with in deep-sea deposits. On pp. 19-23 we have indicated the 
properties most easily observed in free mineral particles, in the form of more or less 
perfect crystals or irregular splinters, that may serve to determine the species. It 
remains here to point out some special characters of volcanic minerals, which permit us 
to distinguish them from minerals of continental origin. Under each species, arranged 
alphabetically, are given the distinctive peculiarities on which we have relied in deter- 
mining the species as having come from recent eruptions. 
Amphibole, Basaltic hornblende, fragments of well-crystallised individuals, sometimes 
regularly-bounded crystals coated with volcanic glass, generally compact, no fibrous 
structure, well-marked cleavage, high lustre on the planes of cleavage, black by reflected 
light, brown or reddish brown by transmitted light, strong pleochroism and absorption, 
zonary structure, numerous vitreous and gaseous inclusions, coating of magnetite and 
characteristic corrosion. Felspars, {a) Monoclinic, Sanidine, often in crystals, with 
glassy habit, colourless and transparent, tabular parallel to M, or elongated parallel to 
the edge P/M, separation-planes parallel to the orthopinakoid, numerous gas and 
vitreous inclusions often crowded together in the same crystal, having sometimes 
geometrical outlines, and often regularly disposed in the interior of the crystal, often 
covered by or imbedded in a glassy coating, (h) Triclinic, Plagioclase, glassy habit, 
transparent, few decomposition products, crystals in the form of thin rhombic tables 
parallel to M, gaseous and vitreous inclusions. Olivine, regularly-formed crystals coated 
with volcanic glass or palagonite, often skeleton crystals, inclusions of vitreous particles, 
rarely decomposed into serpentinous matter, often reddish by decomposition of ferric 
oxide. Pyroxene, (a) Rhombic, Hypersthene, reddish or brownish fragments, or bounded 
by cleavage planes, or vaguely-outlined crystals, prismatic, intergrowth with monoclinic 
pyroxene. Bronzite, glass inclusions, no intergrowth with monoclinic pyroxene. (6) Mono- 
clinic, Augite, often regularly-formed crystals, or fragments coated with volcanic glass, 
fresh, rarely decomposed into chloritic substance or into uralite, frequent glass inclusions. 
Quartz. — In exceptional instances quartz was observed as small crystals bounded by the 
planes of the hexagonal prism and pyramid ; these may have been derived from liparitic 
ashes, or from the disintegration of liparitic rock fragments. In other cases a few quartz 
grains containing glass inclusions were observed, hence in all probability of volcanic 
origin. 
It is evident that the distinctive characters given above are especially in relation with 
the less advanced degree of decomposition, which is itself a consequence of their recent 
eruptive origin. These characters have never been used exclusively, but always in con- 
junction with the mineral associations and positions in the deposits. There are other 
mineral particles in the sediments, which, in the free state, do not offer any distinctive 
