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

others define it as an aggregate of orthoclase, amphibole, and quartz. Some authorities erroneously class the hornblendic granites among the syenytes. Cotta says: "The orthoclase or microcline is usually the principal ingredient, and being in general red, it gives that colour to the whole rock. There

are, however, syenytes whose orthoclase is nearly white." In the syenytes of West Galway, Ireland, of metamorphic origin, the orthoclase is usually white.

Varieties of Syenyte are,—a. Quartzose, and b. Titanitic.

Whinstones, or Greenstones, supposed to be metumorphosed.

H. HORNBLENDE ROCK (Macculloch). An aggregate of amphibole, felspar (usually not orthoclase), pyrite or marcasite, epidote, &c. &c. Some are so finely crystalline as to be nearly compact, while others contain crystals of amphibole, from one to four or five inches long.

Hornblende rock may in places be schistose, or nodular, or concretionary. Some of the schistose portions of this kind of rock, from Iarconnaught, Ireland, have been proved by Forbes to be derivate rocks; consequently such portions must be metamorphosed tuff. When Hornblende rock is nodular. or concretionary, it may have spheroids from the size of a man's head to four or five feet in diameter, irregularly heaped up together, with the interstices filled with a schistose-looking stuff, that has a foliation rudely curling round the nodules; or the interstices may be occupied by a felsitic rock, or even with quartzitic stuff, or perhaps with two or more of these substances mixed together.

Spheroidal or concretionary structure occurs in some whinstones, and Scrope calls particular attention to it, in some of the augytes of Central France. To such a structure in the original (unmetamorphosed) rock, some of that in the Hornblende rock may possibly be due; nevertheless, the greater portion is probably due to the brokenup parts of the flow [the Friction-breccia of Cotta] that were rounded by attrition against one another; while the interstices were filled with the abraded or disintegrated portions of the rock, or by foreign matter washed into them by the water into which the flow was poured. This suggestion appears probable, more especially when the typical rock merges into the nodular variety, and the latter, through agglomerate or conglomerate, into schist and gneiss.

a. Actinolite Rock, or Glassy Actinolite Rock (Krantz).

b. Tremolite Rock.

Hyaline acicular crystals of actinolite or tremolite, respectively mixed with a felspar (usually not orthoclase), or numerous nests of crystals may occur in a hornblendic felspathic matrix.

NOTE.-Actinolite and tremolite rocks are liable to merge into ophyte, or one of the allied rocks, as all the magnesian amphiboles seem to have a tendency to change by pseudomorphic action, partly or wholly into ophite, steatite, or such minerals.

c. Hyperyte, or Hypersthenyte (see ante, page 59). d. Dioryte (see ante, page 59).

e. Syenyte (see ante, page 60).

é. Felso-syenyte, or Felsitic Syenyte, a variety of syenyte, in which the felspar (orthoclase)

predominates to the nearly total exclusion. of the amphibole and other minerals.

f. Mico-hornblende Rock, or Micaceous Hornblende Rock.

Black, bronze, or white mica occurs as an essential. The flakes are sometimes of a considerable size, but more often they occur in small pockets or secretions. Usually they are regularly, although not very abundantly, distributed through the mass.

A mico-hornblende rock is easily distinguished, as the mica decomposes more readily than the other constituents, and gives the rocks a pitted aspect, if the mica is in bunches or pockets; while, if it is in large flakes, the weathered surface of the rock has often a somewhat graphic character, caused by the weathering away of the edges of the mica. Other varieties also have mica as an essential, scattered through the mass; these latter are often more or less schistoid.

G. Rocks due to Pseudomorphic Action, or to Weathering. Some of these rocks, as will be evident from their description, belong in part to Order No. II. (Derivate Rocks); as, however, they are products of the igneous rocks, it seems expedient to describe them altogether,

A. OPHYTE, or OPHITE; SERPENTINE.-A compact rock, dull in fracture, with an unctuous feel. Colour dark green to blackish or brownish, reddish or variegated.

Dana divides massive serpentine into Precious and Common Ophyte. The first "is of a rich oilgreen colour, of pale or dark shades, and translucent even when in thick pieces." The common ophyte is of dark shades of colour, and sub-translucent.

"The former has a hardness of from 2.5 to 3; and the latter often of 4 or beyond, owing to impurities."

Ophyte may originally have been either whinstone or felstone. It weathers into an impure ferruginous meerschaum of a dirty yellowish colour, giving the rock a peculiar burnt or baked aspect.

A variety is Ophi-hornblende rock, or a hornblende rock in which part of the felspar or part of the amphibole is changed into ophyte.

B. STEATYTE, Soap-stone.-An unctuous, soft, fissile, but, at the same time, tough rock, of a light greenish, greyish, or bluish colour.

Ophyte and steatyte often occur together in intrusive masses or dykes, associated with steatitic felstone or ophi-hornblende rock, also with hornblende schist or felsitic schist. Friable felstone, felstone tuff, whinstone tuff, &c., may change into steatyte.

Varieties are,-a. Felspathic; b. Pyroxenic; and c. Amphibolic.

Steatyte, as formed from felstone or whinstone, may contain a large percentage of felspathic tuff, or of pyroxene or amphibole.

C. EKLOGYTE, or EKLOGITE.-An aggregate of green smaragdite and red garnets. The smaragdite forms a finely crystalline matrix, in which the crystals of garnet are disseminated. It is often micaceous. Some varieties undoubtedly are pseudomorphs of hornblende rock.

NOTE. Some of the fissile rocks, usually called Eklogyte, are metamorphic sedimentary rocks, and their description is given under the head of Smaragdite Schist (see page 93). The rock here described is an intrusive rock.