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times being parallel, or nearly so, to the walls of the dykes, but at other times they are oblique. The bands are due to thin zones of different colour or texture, perhaps also of composition. In these bands, or between them, there is on rare occasions a structure like foliation.

All the metamorphosed igneous rocks are more or less granitoid, in accordance with the intensity of the metamorphism that has acted on them and the associated sedimentary rocks.

C. Protogene [Gr. protogenes, first formed; the rock, when first discovered, being supposed to be the oldest].-A granitoid rock; a crystalline aggregate of quartz, felspar, and talc.

Protogene, although not a true granite, seems allied to those of the Oligoclase type (B). The name is said to have been given originally to a metamorphic rock, but its original signification appears to have been lost, for Cotta thus describes it :-" A granite which contains talc or chlorite, or decomposed mica, instead of the usual mica." This is an erroneous definition, for if it contains either mica or ripidolite instead of talc, it cannot be Protogene.* However, Cotta would appear not to be the only geologist or petrologist who has found this rock a stumbling-block; as Haughton, after examining numerous specimens of the so-called Protogene from the Alps, states that most of them contained not talc, but dull mica or ripidolite, or some kindred mineral." If a rock contains mica in addition to talc, or ripidolite in place of talc, it cannot be protogene, but is, in the one case, Talcose Granite, and in the other, Chloritic or Ripidolitic Granite.

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* Some basic felstones, when metamorphosed, appear to be true protogene (quartz+felspar+talc).

The formation of granite is not fully understood; yet I cannot but believe that while some are undoubtedly intrusive, others have been formed by extreme metamorphic action. However, between the two extremes there is a rock (previously mentioned and described as Intrusive oligoclase granite) that partakes of the nature of both, having constituents very similar to the ordinary oligoclase granite, while it is intrusive, like the highly siliceous granite. This at first may appear an anomaly; nevertheless it seems capable of a simple explanation.

All authorities infer that granites were formed at a considerable depth beneath the earth's surface, under pressure, by extreme heat. They cooled and consolidated, more or less gradually, long previous to coming near, or being exposed at the surface of

the earth.

Rocks, under the above conditions, would melt more or less rapidly in accordance with the intensity of the heat to which they were subjected, the amount of pressure, and constituents of which they are composed. Moreover, the more acid portions would remain longer fluid, during refrigeration, than the basic (see page 28).

If, while in a state of fusion, the heating action were to cease or begin to subside (either of which must at some time have happened), the rocks or strata affected would be in the following conditions: Part would be entirely fused or liquefied; part would be semifused; while the rocks adjacent to the latter would be only more or less altered. Of the latter class, the least altered rock would be represented by rocks belonging to the Schist series; while the more altered rocks, according to the intensity of the metamorphic action, would form the Gneiss

series and the Gneissoid granite. The second class, or the semifluid rocks, would form the Oligoclase granite, or the Granite due to extreme metamorphism; while the first class, or the completely fluid mass, would form the different intrusive or irruptive rocks.

Of the completely fluid mass, part ought to find its way to, or close to, the earth's surface, and then cool under little or no pressure, forming the Plutonic and Volcanic rocks; a portion would consolidate between the source, the caldron, if it may be so called, and the surface of the earth, under more or less pressure, and form Elvanyte or Quartz-Porphyry, the granitic rocks next to be enumerated and described; while the residue would consolidate in or near the caldron.

The consolidation of the residue, that remained in or near the caldron or source, could scarcely have been simultaneous, as it is probable the outer or upper portion would consolidate sooner than the inner or lower part. Moreover the acid portion would consolidate slower than the basic part; consequently there ought to be two distinct rocks forming,-a more basic rock above, and a more acid or siliceous rock below. As the upper or more basic rock cooled and consolidated, it ought to shrink more or less, and thereby form cracks, fissures, and other vacancies, into which the underlying still fluid or semifluid matter would be squeezed; therefore at any time prior to their final. consolidation, part of the oligoclase granite or part of the highly siliceous granite might be forced up into and occupy all vacancies in the supercrescent rocks, and thereby form intrusive grauite of one or both types (Intrusive oligoclase granite and Intrusive

highly siliceous granite);-subsequently, when the overlying rocks were denuded away, tracts, veins, &c., of these granites would be exposed.

The above suggestions, if correct, give a solution for the formation of the three different kinds of granite,-Highly siliceous granite, Intrusive oligoclase granite, and the Non-intrusive oligoclase granite. The Non-intrusive oligoclase granite would be represented by the semifluid portion that first consolidated; the Intrusive oligoclase granite by the more basic portion of the fluid mass that was forced out of its normal position; while the Highly siliceous granite would be the part that took longest to cool and consolidate. That granite must cool and consolidate under laws somewhat similar to the above appears highly probable, because when two or more granites come from one source, the last formed is more siliceous than the rock through which it breaks up, while the veins of segregation in the former are more siliceous than the parent rock in which they appear.

D. Elvanyte (Jukes); Quartz-Porphyry; Quartziferous Porphyry; Granitic Porphyry (Cotta), [Celtic, el or oil, rock, and van or ban, white, so called from the white crust of the rock when weathered]. -A granitic rock, having a granular or compact felsitic or felspathic matrix, inclosing globules, blebs, and crystals of quartz, crystals of one or more felspars, with more or less mica or amphibole, ripidolite, and the like. Pyrite and marcasite are often constituents. In many of the siliceous varieties, a considerable portion of the quartz crystallized out prior to the other minerals. The matrix may be siliceous (felsitic) or basic (jel

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spathic), and of a greenish, greyish, brownish, blackish, bluish, or even yellowish colour: all of the yellowish, as also some of the blues, seem due to weathering.

NOTE.Elvanyte naturally includes not only the quartzporphyries, but also the syenytes (quartz+felspar+amphibole) of some British geologists.

The free silica or quartz in the Elvanyte is for the most part in irregular blebs or globules, from minute specks to the size of a pea, or even larger. The quartz internally has a glassy, often radiated structure, and externally on some, the crystal faces can be recognized, while others appear to be regular coated minute balls. The quartz is scattered through the mass, sometimes sparingly, but at other times so thickly as to give the rock a pisolitic aspect. Elvanytes, except some of the very granitic varieties, weather with the even flowing surface so characteristic of the Felstones, and not with the rough rugged aspect of granite. They often near the edge of large masses, at the walls of dykes, and in small branch dykes or veins merge into a rock in appearance identical with felstone this compact rock is called by Cotta the Base or Mother-rock. The Mother-rock at dyke walls is rarely more than a few inches thick. Elvanytes being hypogene rocks, are never accompanied by tuff.

NOTE. A true elvanyte is more crystalline at the centre of a dyke or mass than at the margins, while an elvanoid rock due to metamorphism is more crystalline at the margins than in the interior, the change in the latter taking place from the outside inwards.

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