included all the very basic Plutonic rocks. They are usually dark-coloured, greenish or blackish; however, a few are light-coloured. The whinstones are often vesicular or amygdaloidal, and have their associated tuffs, with which they are often interstratified.

A. DOLERYTE [Gr. doleros, deceptive].-A tough aggregate, principally a mixture of felspar and pyroxene. Nearly always of a dark colour. a. White-rock (Jukes).-A doleryte of a nearly white colour, found associated with coal in Staffordshire and elsewhere. The dykes of "white-rock" can be traced into masses of. ordinary dark-coloured doleryte.

b. Aphanyte-doleryte; Basalt. - Very compact; often called "Basalt;" the latter name, however, ought to be only used for a variety of volcanic rocks.

B. MELAPHYRE.-A crystalline aggregate of felspar and pyroxene, with or without amphibole; of a dark colour, greenish, brownish, or blackish, with more or less resinous lustre; may be compact, porphyritic, vesicular, or amygdaloidal, and often contains specks of opal or quartz, also zeolites. Before the blowpipe it fuses readily; fracture uneven.

Varieties in Composition.

a. Eukryte, or Eukrite.-A crystalline granular
aggregate of anorthite and pyroxene, occa-
sionally with some olivine, amphibole, and
epidote; the latter mineral being due to
decomposition.

Peridolyte.-A subvariety in which olivine is
always present.

b. Magnetic Melaphyre; having magnetite as a constituent. This rock may always be distinguished from magnetic diabase, as the magnetic constituent of the latter is pyrrhotite.

c. Micaceous Melaphyre.-The mica often is in considerable quantities.

Structural Varieties.

d. Porphyritic, containing felspar crystals; e. Amygdaloidal; f. Vesicular; and g. Variolitic, having spots of a different colour and texture, also perhaps of composition.

C. PYROXENYTE (Dana).-A compound of pyroxene and orthoclase.

D. DIABASE.-A crystalline granular aggregate of felspar, pyroxene, and ripidolite; colour usually greenish or purplish. The felspar is either oligoclase or labradorite, and frequently the latter. The pyroxene is diallage, and rarely ferruginous. The ripidolite is generally green, and in subordinate quantities; it is often only distinguishable with difficulty, from being in intimate admixture with the diallage.

Varieties in Composition.

a. Pyroxenic, or Angitic Diabase, having numerous and well-developed crystals of pyroxene, which, when weathered, give the rock a spotted appearance like a toad.

b. Uralitic Diabase, with numerous and welldeveloped crystals of uralite. In some subvarieties part of the pyroxene in the matrix is replaced by uralite. This rock, also, when weathered, has a spotted aspect.

c. Labradoritic; d. Oligoclasic; e. Magnetic, containing pyrrhotite; a micaceous subvariety, weathers freely into a magnetic sand; f. Kersantyte (Delesse), or Micaceous; and g. Calcareous." In a fine-grained or compact matrix of diabase rock are found small rounded grains of calcite, which do not apppear to be the fillings-up of cavities."Cotta.

Structural Varieties.

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If diabase contains numerous and well-developed crystals of felspar, it is called h. Porphyritic; if there are roundish concretions of any mineral, it is called i. Amygdaloidal; while it is j. Vesicular, if there are open cavities; k. Variolitic ("In the principal mass round concretions occur of a compact or radial-fibrous, or concentric felsite (labradorite) ' -Cotta); and l. Aphanyte, or Compact Diabase. E. GABBRO; GRANITONE; DIALLAGE ROCK-"consists of labradorite or saussurite, and diallage, or smaragdite irregularly combined; also sometimes all of these minerals together. It is very coarse-grained, fine-grained to compact, sometimes slaty or spotted."- Cotta.

Some Diallage rock, such as that of the Lizard, Cornwall, is a metamorphosed igneous rock. a. Euphotide.—" A combination of felspar (saussurite) and diallage, with titaniferous and chromic magnetic iron-ore, pyrite, serpentine, and carbonates. The diallage often. occurs as the variety smaragdite."-Cotta. b. Noryte, or Norite (Scheerer), Labrador Rock."The Noryte of Scheerer, not of Esmark, is a compound of hypersthene or diallage,

labradorite, orthoclase (containing soda), and even some quartz."-Cotta.

Sterry Hunt has described rocks under the name Anorthosyte. Of these, some contain a felspar between andesine and anorthite, some between andesine and labradorite; while in others it is a pure labradorite.

Many of these rocks (a and b), if not all of them, may more properly belong to the metamorphic igneous rocks.

c. Hyperyte, or Hyperite; Hypersthenyte.

The hyperyte of Cotta and Dana is a coarsegrained to compact aggregate of labradorite and hypersthene.

Some varieties are said to occur as unaltered igneous rocks, but many of the coarse crystalline varieties would appear to belong to the metamorphic igneous rock series.

F. DIORYTE, or DIORITE [Gr. dioros, a clear distinction, in contradistinction to the doleryte, in which the minerals are indistinct].-A crystalline granular compound of felspar (not orthoclase) and amphibole. Sterry Hunt has called this rock Anorthyte.

Many diorytes are undoubtedly metamorphosed igneous rocks. In them the minerals are always prominently and distinctly visible; therefore it does not appear at all improbable that they were the rocks which first received this name. According to Dana, the felspar ought to be albite. He however seems to be nearly alone in this opinion.

a. Amphibolyte. A homogeneous fine-grained compact mass, consisting of labradorite and

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amphibole (Dana). According to Naumann, the latter ought greatly to predominate. b. Aphanyte [Gr. aphanes, unmanifest], or Anamesyte (Jukes).-A compact homogeneous variety of dioryte, without distinct grains. Some dioryte-aphanytes are said to have as their felspar, orthoclase; in which case they are not, properly speaking, a homogeneous variety of Dioryte, but a homogeneous variety of Syenyte.

c. Kersanton (Riviere), Micaceous Dioryte.-Containing a great and conspicuous quantity of mica.

NOTE. The highly micaceous diorytes, similarly as the highly micaceous melaphyres and diabases, would be classed by some geologists among the "mica traps."

d. Napoleonyte, or Orbicular Dioryte.-A local variety, consisting, according to Delesse, of a combination of anorthite, blackish-green amphibole, with some quartz. The anorthite and amphibole form orbicular concentric layers round a kernel, each mineral forming different layers of alternate light and dark colour.

G. SYENYTE, SYENITE.-A crystalline aggregate of orthoclase and amphibole, with or without quartz. The quartz appears to be more an accessory than an essential.

NOTE. Some syenytes are undoubtedly metamorphosed igneous rocks, while others do not appear to have had such an origin.

The name Syenyte has been given to various rocks. Haughton, Forbes, Cotta, Werner, and others describe it as a rock in which quartz is not a necessary ingredient; while Jukes, Dana, and