REPORT ON THE DEEP-SEA DEPOSITS. 
825 
probabDity that these minerals have been derived from the disintegration of rocks found 
at the surface of the continents. These determinations rely not so much upon any 
isolated characters, as upon the union of a variety of conditions, such as geographical 
position, size and form of the grains, specific nature of the minerals, characters indicating 
the mode of transport, and especially the lithological and mineralogical associations. 
After these general remarks we may give an enumeration of the principal species of 
minerals which are considered as having a terrigenous origin, along with some of their 
most striking peculiarities. It must be remembered, however, that these characters are 
not absolute, and that their value is important only when taken along with associated 
rocks and minerals. 
Amphibole, Common Hornblende, generally greenish, rarely brownish, more or 
less distinctly prismatic, fibrous structure, rarely zonary or containing inclusions, 
cleavage planes not well marked nor very shining, associated with debris of crystal- 
line or schisto-crystalline rocks. Actinolite, found as columnar or fibrous aggregates, 
associated with large fragments of actinolite-schists. Glaucophane, small prismatic 
fragments, pronounced violet-blue colour, associated with land debris and fragments 
of mica-schists and gneissic rocks. Apatite, although mineralogically no distinction 
possible from apatite derived from volcanic rocks, the larger grains of this mineral, 
often elongated or rounded fragments, occur associated with debris of older rocks. 
Calcite, fragments of compact limestones. Chlorite cannot be determined by its 
proper characters as originating from older rocks, but frequently occurs with debris 
of schistose rocks, with amphibolic or schistose fragments, also as coatings of some 
continental rocks and minerals. Chromite, with debris of olivine rocks. Dolomite, 
as fragments of dolomitic limestones and dolomitic rocks, with blocks and gravel 
of older eruptive and sedimentary rocks transported by icebergs. Felspars {a) Mono- 
clinic, Orthoclase, generally fragments bounded by cleavage planes following P and M, 
often altered grains, no glassy habit, dull and milky, no glass inclusions, some liquid 
inclusions, intergrowth with quartz or with triclinic felspar, decomposition into kaolin 
or muscovite, no zonary structure nor fissures as in sanidine, associated in the deposits 
with debris of crystalline schists, and principally with older eruptive rock fragments. 
(6) Triclinic, Microcline, always associated with debris of continental origin. Plagio- 
clase, duU and cloudy, generally altered, associated with debris of older eruptive rocks. 
Garnet, although mineralogically no distinction possible, must be of continental origin 
when coated with green chloritic or serpentinous substance or phyllitic matter, and 
occurring with fragments of schisto-crystalline rocks. Glauconite} Magnetite cannot 
be distinguished from the same mineral in the recent volcanic rocks and particles, 
but often associated with land debris. Mica, White Mica, always associated with older 
eruptive rocks and continental debris ; Sericite, associated with fragments of schistose 
^ See Chemical Deposits, Chapter VI. 
