184 REPORT — 1860. 



rocks; and the earthy minerals imbedded in the metamorphic strata around 

 such rocks resemble quartz in being simjile crystallized oxides, — innumerable 

 gems, for instance, of the crystallized oxide of alumina — vast masses of the 

 same, many tons in weight, in the form of emery, encysted in limestone 

 which has been metamorphosed by rocks of granitic character, — still greater 

 masses of crystalline sesquioxide of iron in similar relation to those rocks, — 

 crystalline peroxide of tin shot through them into the strata above. 



In the eruptive rocks which followed the quartzose, these minerals, with 

 almost all the quartz, died out, and were succeeded by others of a more 

 complex nature appropriate to the porphyritic, trachytic, basaltic, and lavic 

 eruptions. Yet all these, as well as the granitic, are attended by similar 

 metalliferous veins, which grow very weak in the latest, but still show, at least 

 as far as the eruption of the more ancient lavas*, a continued communica- 

 tion with a common reservoir deeper seated than any of them. 



Davy saw the lava of Vesuvius issuing, as if forced up by elastic fluids, 

 perfectly liquid, and nearly white-hot, its surface in violent agitation, with 

 large bubbles rising from it, which emitted clouds of white smoke, consisting 

 of common salt in great excf ss, much chloride of iron, and some sulphate of 

 lime, accompanied with aqueous vapour, and with hydrochloric and sul- 

 phurous acids. It contains also realgar and sulphide of copper, due pro- 

 bably to the reaction of sulphuretted hydrogen on the chloride of the metal. 



In the early time of these eruptive emanations, when they escaped at 

 many points with little interruption, the land rose only to low levels above 

 the waters. As the crust of the earth grew more solid and weighty, and 

 the vent was confined to fewer lines of shrinkage, the elastic elements of 

 disturbance upheaved the incumbent beds with greater power, and the 



* Though the presence of quartz in lava has been denied, the following account of its 

 coexistence with schorl in that of the valley of Maria in Lipari by Spallanzani shows that it 

 does exist in ancient, perhaps basaltic, lavas, and strikingly illustrates the theory of its sub- 

 limation, as here advanced. " Among the lavas partly decomposed we find pumices and 

 enamels containing felspars and scales of black schorls, and certain curious and beautiful 

 objects, which derive their origin, in my opinion, from filtration. The lava is white and friable 

 to a certain depth, of a petrosiliceous base, full of small cells and cavities, within which these 

 objects make their appearance : — First, minute crystals of schorl ; from the inside of these 

 cells project very slender schorls, sometimes resembling minute chestnut bristles, sometimes 

 a bunch, a plume, or a fan, to be ascribed to filtration after the hardening of the lava, since 

 though it is common to find schorls in lavas, they are found incorporated within them, not 

 detached as in this ease. The second filtration has produced small quartzose crystals, and 

 the manner of their distribution in prodigious numbers renders them a very singular phe- 

 nomenon among volcanic objects. Wherever the lava is scabrous, wherever it has folds, 

 sinuosities, cavities, or fissures, it is full of these crystallizations. The larger crystals extend 

 to 3^ lines, the greater part about \ a line. Tiiey consist of a hexagonal prism, infixed 

 by the base into the lava, and terminated by a similar pyramid. Three crystals, among those 

 I examined, were terminated by two pyramids, the prism being attached to the lava by a 

 few points, and the prisms projecting out. The most regular are in small cavities, but not 

 a few are on the surface of the lava. The. lava, embellished with these, forms immense 

 rocks and vast elevations hanging over the sea, which, whenever they are broken to a certain 

 depth, are found to contain these crystals, with capillary schorls, not \ery numerous. I have 

 in my possession a group of needle-formed crystals from Mont St. Gotliard, within which 

 are seven small prisms of black striated schorl. The same may be observed in these minute 

 crystals. One of these ivas perforated from side to side by a needle of schorl, the two ends 

 of which projected out. The formation of these capillary schorls must have preceded that 

 of the cpiartzose crystals ; otherwise it is impossible to conceive how the former should have 

 penetrated the substance of the latter. In rcmelting the lava in a furnace, the quartz 

 crystals remained perfectly unaltered." 



Spallanzani also states, that in this lava are garnets and chrysolites more refractory in the 

 fire than the matrix ; and he adds that since Dolomieu's visit to the adjoining stoves, when 

 the whole ground on which they stood was saturated with hot vapours issuing everywhere 

 from small openings an inch or two in diameter, at the time of his own visit these were 

 reduced to one, exhaling some sulphur and encrusted with soft pyrites. 



