mass, namely, the variety of their composition: "If the unstratified rocks were all derived from the same melted mass in the earth's interior, we should suppose they would not differ from each other at any period of their eruption. But in fact they do so differ as to show, first, that the ingredients from which they were derived were different; and secondly, that the circumstances under which they were formed, as to temperature, fusion, and pressure were different."

Next followed the discovery that all the constituents of granite existed in the sedimentary rocks, and could be actually manufactured out of them.f Then, in the progress of exploration, water-marks were discovered in mica schist, heretofore regarded as an igneous rock, and fossils were found in other so-called plutonic rocks. Then the discovery of graphite in granite was declared by eminent chemists inconsistent with melting heat. "The presence of graphite (black lead) in granite, gneiss and diorite," says an eminent chemist, "has renewed the dispute between the neptunists and the plutonists. Graphite is known to be nearly pure carbon, for it leaves in burning but a very small quantity of ash. Now, if these primitive crystalline rocks are of igneous formation, it is impossible to explain how graphite could co-exist with silicates of protoxide of iron, without having reduced these salts; judging merely by what takes place in blast furnaces, since carbon reduces all oxides of iron at a high temperature. It must then be admitted that granite, gneiss, and diorites did not contain graphite when the mineral elements of these rocks, such as mica, hornblende, and other silicates were in a state of fusion. Graphite, then, must have been subsequently introduced into these

*Geology, p. 92.

† Annual of Scientific Discovery, 1861, p. 279, and 1865, p. 312.

Ibid. 1864, p. 241.

rocks; but when and how? Questions like these are difficult to answer. The most plausible hypothesis is by the wet way into the crystalline rocks, and substituted for one of the mineral components. Thus in the gneiss of Passan it takes the place of mica."*

Then came the discovery of magnetic iron ore in plutonic rocks, and even of fossils. "At the recent meeting of the London Geologists' Association, Mr. Tomlinson, after adverting to the close resemblance or identity of the slags and dross of iron furnaces with naturally-formed volcanic rocks-as lava, pitch-stones, etc.-stated, that while we may regard the plutonic origin of such rocks as certain, it should be borne in mind that volcanic rocks formed but a small proportion only of the rocks termed plutonic, or fire-formed. All granites, and certain porphyries, were generaliy regarded as fused by such action at great depths. But as many of these rocks contained magnetic iron ore they could not be the results of fusion, else their composition would be that of a vitreous, instead of a crystalline, rock. In cooling, quartz and iron would not separate, the oxides having a strong affinity for silica. Another difficulty which presented itself to the mind of the plutonist was, that fossil forms were occasionally met with in magnetic iron ore; as the Devonian Brachiopod Spirifer Speciosus, which was thus found in a quartz rock mixed with iron pyrites. Such facts pointed more to a neptunistic than to a plutonic origin for granite, quartz, and other allied rocks."

The same conclusion results from a comparison of the specific gravity of quartz with feldspar. The quartz being the heaviest must have sunk to the bottom of the molten mass, as water sinks through oil; and we should find it, not scattered in crystals through the granite, but all in one mass at the bottom. Accordingly we find Von * London Chemical News, cited in Annual of Scientific Discovery, 1865, p. 219.

Fuchs deciding absolutely against the igneous theory. "He reasoned against the view that the crystalline rocks were once in a state of fusion, as follows, using granite as an illustration: If granite were once in a molten condition, then, as it cooled, in the first place, quartz must have crystallized out, and would have sunk down through the still molten mass, while feldspar and mica must have crystallized at a much later stage of cooling, as the necessary consequence of their different degrees of fusibility. Further, the inclusion of arsenical pyrites, sulphide of antimony, tourmaline, garnet, fluor spar, etc., by quartz is incompatible with the crystallization of the latter from a state of igneous fusion. He proceeds to show that amorphous must precede crystalline rocks, and that originally the solid part of the earth consisted of silica and silicates in the amorphous form, while the liquid portions were largely made up of solutions of lime and magnesia, and their carbonates." This is merely a translation of the second verse of Genesis into scientific language.

Thus far the steady progress of discovery was an accumulation of facts disproving the igneous formation of the crystalline rocks, under known chemical and mechanical conditions, against an unproved assumption that granite was an igneous formation. Not a single fact supporting the assumption had ever been presented, save our ignorance of the interior of the earth, and the assumption that every thing must be melted by extreme heat down there. Attempts were made, however, to imitate the subterranean conditions of heat under pressure. Experiments were made to ascertain the effect of pressure on melting bodies; and it was found by Hopkins that immense pressure prevented their melting, unless at greatly increased heats. Next, experiments were made * Annual of Scientific Discovery, 1858, p. 301.

by Daubree, and others, to melt quartz by igneous fusion, which settled forever the question as to the heat of the melting point in the simplest manner; namely, that it would not melt at all, but that its crystals would decompose, and the mass become lighter in the fire, as all clayey substances do; or, where there was sufficient alkali, would form a black glass, of quite a different structure and specific gravity from granite.* The product of the igneous fusion of the materials of granite is not granite at all, any more than the ash and cinder of coal is coal, or than a glass tumbler is silex. It is a different substance.

Dr. Percy, of the London School of Mines, in a recent lecture, objected to the assertion of geologists that granitic rocks must have been formed by plutonic agencies; for, said he, "There are certain difficulties which have always stood in the way of accepting this view of the subject—difficulties known to those who have been accustomed to make experiments on the fusion of mineral substances at high temperature. This is especially seen by examining the condition of quartz in granite; it is always found in the crystalline condition, and has invariably a specific gravity of 2.6. There is not a single instance known to the contrary. Hence there is reason to believe that the quartz could never have been fused; for the moment silica is fused, no matter in what condition it was previously, a peculiar glass-like, colloidal mass is produced, having a specific gravity which never exceeds 2.3. Therefore there is good reason to conclude that granite could never have been formed under the conditions of a high temperature."

It only remained now to show how granite was formed, in the wet way, from the sedimentary rocks; and this demonstration has been given, and the granite actually manufactured accordingly. T. Sterry Hunt, F. R. S., of

Annual of Scientific Discovery, 1861, p. 279.-1865, p. 301.

the Canada Geological Commission, in a paper on The Theory of the Transformation of the Sedimentary Deposits into Crystalline Rocks, thus explains the matter: "We can not admit that the alteration of the sedimentary rocks has been effected by a great elevation of temperature, approaching, as many have imagined, to igneous fusion; for we find unoxidized carbon in the form of graphite both in beds of crystalline limestone and in beds of iron ore; and it is well known that these substances, and even the vapor of water, oxidize graphite at a red heat, with formation of carbonic acid and carbonic oxide. I have, however, shown that solutions of alkaline carbonates, in presence of silica and earthy carbonates, slowly give rise to silicates with disengagement of carbonic acid, even at a temperature of 212°; the alkali being converted into a silicate, which is then decomposed by the earthy carbonate regenerating the alkaline salt, which serves as an intermedium between the silica and the earthy base. I have thus endeavored to explain the production of the various silicates of lime, magnesia, and oxide of iron, so abundant in crystalline rocks; and with the intervention. of the argillaceous element, the formation of chlorite, epidote, and garnet. I called attention to the constant presence of small portions of alkalies in insoluble combination in these silicates a fact which had already led Kuhlmann to conclude that alkaline silicates have played an important part in the formation of many minerals; and I suggested that, by combining with alkalies, clays might yield feldspars and micas (the chief ingredients of granite), which are commonly associated in nature with. the silicates above mentioned. This suggestion has been verified by Daubree, who has succeeded in producing feldspars by heating together for some weeks, to 400° C., mixtures of kaolin and alkaline silicates in the presence of water. The problem of the generation from the sands,