HISTORY OF CRYSTALLINE ROCKS. 23 
§ 38. The genesis of rocks like phonolite, which are essentially made up of a feld- 
spar having the orthoclase-ratios, with an admixture of a more basic silicate, as nephelite 
or a zeolite, can, however, hardly be explained save as an educt of crenitic action, like tra- 
chyte and granite. It represents, however, a period in the history of the plutonic mass 
when, from a diminution of silica, the production of quartz ceases, and more basic feld- 
spathic or zeolitic compounds begin to replace the orthoclase. When, from compounds 
like these, in which the proportion of protoxyds to alumina falls below the normal 
oxygen-ratio of 1: 3, we pass to those, like the muscovitic micas, most tourmalines, and 
the pinite-like minerals, with a diminished proportion of protoxyds, we have probably in 
all cases to do either with crenitic products or with the direct results of subaerial decay. 
§ 39. Fouqué and Michel Lévy, in their recent experiments, have shown us how to 
form artificially, from mixtures in igneous fusion, in which the proportions of elements 
were prearranged, crystalline aggregates containing leucite with labradorite, pyroxene, 
magnetite, and spinel, and others holding chrysolite in similar associations. The problem 
which lies behind this discovery is to determine how the materials are so grouped in 
nature’s laboratory as to yield the mixtures necessary, in the one case, for the production 
of a leucitophyre, and in the other for a chrysolitic dolerite. The research of the natural 
processes by which these combinations are reached has been the object of the preceding 
inquiry into the results of eliquation, on the one hand, and of the solvent and replacing 
“action of percolating waters, on the other. 
§ 40. It is farther to be noted that the experiments of Fouqué and Michel Lévy were 
made by the slow cooling of mixtures from simple igneous fusion, and the question must 
here be raised how far these reactions would be affected by the intervention of water ; in 
other words, whether, as maintained by Poulett Scrope, Scheerer, Elie de Beaumont, and 
many others, water is not always present in the mass of igneous rocks. So far as experi- 
ments go, the process of cooling from simple igneous fusion would seem to be inadequate 
to account for the origin of many of the minerals of eruptive rocks. Fouqué and Michel 
Lévy inform us that they “ have vainly sought to produce, by igneous fusion, rocks with 
quartz, orthoclase, albite, white or black mica, or amphibole,” although the occasional 
accidental production of orthoclase as a furnace-product has been noticed. The presence 
of albite in the recent lavas of Santorin, in association with labradorite, pyroxene, and 
chrysolite, has been shown by Fouqué (§ 32), and its probable occurrence in a diabase has 
been pointed out by Hawes.’ Both orthoclase and albite have, however, been formed in 
the wet way, at elevated temperatures, under pressure; and pyroxene, while readily 
generated from the products of igneous fusion, was got by Daubrée by the action of super- 
heated water on glass, at the same time with crystallized quartz and magnetite or spinel. * 
The frequent occurrence of pyroxene in veinstones, in intimate association with ortho- 
clase, quartz, apatite, and calcite, suffices to show its aqueous origin, in common with all 
of these species. In like manner, magnetite, which is readily formed in fused basic mix- 
tures, is found crystallized with orthoclase and quartz, with apatite and pyrite, in granitic 
veinstones. Moreover, the fact of its association with garnet, and with zeolitic minerals, 
in the secretions of basic rocks suffices to prove that magnetite, as well as hematite, may 


! Synthèse des Minéraux et des Roches, p. 75. * Trans. Roy. Soc. Canada, Vol. ii. See. iii. p. 39, 
3 Ibid., p. 44. 
