as a general term for the whole suite of basaltic rocks by many
geologists and travellers (_e.g._ trap-dikes, the "traps" of the Deccan).

In the early years of the 19th century a great controversy convulsed the
geological world as to the origin of the older basalts or "floetz-traps."
Werner, the Saxon mineralogist, and his school held them to be of aqueous
origin, the chemical precipitates deposited in primeval seas, but Hutton
and a number of French geologists maintained that they were really volcanic
rocks emitted by craters now extinct (see GEOLOGY: _Historical_).

Of the less common minerals of basalt, a few may be mentioned. Black
hornblende, dark brown in thin sections, and often corroded, is not
uncommon, especially in intrusive basalts. Hypersthene occurs also, usually
replacing olivine. Black mica (biotite) is not infrequently to be seen.
Sapphire, garnet and zircon are rare. Minerals of the felspathoid group
occur in a large number of basaltic rocks; nepheline and leucite are the
most common, but hauyne is occasionally present. If nepheline entirely
replaces felspar, the rock is known as nepheline-basalt; if the replacement
is only partial the term nepheline-basanite is used. Similarly there are
leucite-basalts and leucite-basanites. The nepheline is in small six-sized
prisms, and usually cannot be detected with the unaided eye. Even with the
help of the microscope nepheline basalts are not always easy to determine,
as the crystals may be exceedingly small and imperfect, and they readily
decompose into analcite and zeolites. In some cases only the presence of an
anisotropic substance, with weak double refraction and readily attacked by
acids (the so-called "nephelinitoid"), can be made out. This substance may
be imperfectly crystallized nepheline, or a peculiar glass which is rich in
soda. Most nepheline basalts are fine grained, very dark coloured rocks,
and belong to the Tertiary period. They are fairly common in some parts of
Germany and occur also in Tripoli, Asia Minor, Montana, Cape Verde Islands,
&c. Leucite-basalts contain small rounded crystals of leucite in place of
plagioclase felspar. Rocks of this group are well known in the Eifel, and
other volcanic districts in Germany, also in Bohemia, Italy, Java, Montana,
Celebes, &c. The minerals hauyne, nosean, sodalite and melilite tend to
occur with some frequency in nepheline and leucite-basalts, though rare in
ordinary basalts. Melilite, a lime-alumina-s