OEIGIN OF CEYSTALLINE EOCKS. 33 



tion of the anhydrous rock, a condition which has been designated one of aqueo-igneous 

 fusion. This interposed water, u.nder the influence of great heat and pressure, we may- 

 suppose, with Scheerer, to constitute a sort of granitic juice, which, exuding from the mass, 

 might 1Î11 fissures or other cavities, alike in the granite and in the adjacent rocks, with 

 the characteristic minerals of granitic veins. This seems to have been essentially the view 

 of Élie de Beaumont, who described the elements of the pegmatites, the tourmaline- 

 granites, and the veins, often abounding in quartz, which carry cassiterite and columbite, 

 as emanations from the adjacent granitic masses, or as a granitic aura. Daubrée and 

 Scheerer, in previously describing the similar granitic veins found in ScandinaAaa, con- 

 ceived them to have been filled in like manner, not from an iinstratified granitic sub- 

 stratum, but from the crystalline schists which enclose them." 



§ 65. In both of the above hypotheses, we note that the source of the orthoclase and 

 the quartz of the veins is sought in the solutions derived from the granitic substratum 

 or its closely related crystalline schists. If now we go farther back, and ask for the origin 

 of this granitic substratum, with its constituent minerals, we have shown, in opposition to 

 the view that it is the outer layer of a cooling globe, good reasons for maintaining, in the 

 first place that such a layer must have had a very difierent composition from that of gra- 

 nite, and in the second place that granite itself is a rock of secondary origin, in the forma- 

 tions of which water has in all cases intervened. We have, moreover, already sought to 

 show that the attempt to derive this granitic rock, by any process of metamorphosis or 

 metasomatosis, from sediments formed from the primitive quartzless rock, was untenable, 

 and that the vast granitic substratum, so homogeneous and so widely spread, could not thus 

 have originated. Already, in 18t4, it had been declared that the process which generated 

 the orthoclase and the quartz of the granitic rocks was one represented in more recent 

 times by the production of zeolites. 



§ 66. The generation from basic rocks, by aqueous action, alike of orthoclase, of quartz, 

 and of zeolites, is well known. These are often associated in such rocks, under conditions 

 which show them to be secretions from the surrounding mass. The substance named 

 palagonite is an amorphous, apparently colloidal, hydrous silicate, the composition of which, 

 deducting the water (about seventeen per cent, on an average), is, according to Bunsen, 

 identical with that of his normal pyroxenic or basaltic magma (§ 24), except that the 

 iron in palagonite is in the state of peroxyd. This substance is changed by no great eleva- 

 tion of temperature into the zeolite, chabazite, a crystalline silicate of alumina and alkalies, 

 rich in silica, but destitute of iron-oxyd and magnesia, and a more basic residiuim, in which 

 the latter two bases are retained. Basaltic rook is, according to Buuseu's observations in 

 Iceland, changed through hydration into palagonite, " under the influence of a neptunian 

 cause," and this, by the heat of contiguous eruptive masses, is subsequently transformed 

 into a zeolitic amygdaloid. These operations, as he has shown, may be repeated in our 

 laboratories. Fragments of amorphous native palagonite, when rapidly heated in the flame 

 of a lamp, develope in their mass cavities filled with a white matter, recognized by the aid 

 of a lens as crystalline chabazite ; while the transformation of basaltic rock into palago- 



" For a general account of the views described in this paragraph, and for references to the somewhat extended 

 literature of the subject, see Hunt, Cliemical and Geological Essays, pp. 188-191 ; also Ibid., p. 6. 



Sec. III., 1884. 5. 



