CRYSTALLIZATION OF IGNEOUS ROCKS. 
93 
Part II.—Causes of Crystallization. 
Artificial Production of Pocks and Minerals .—Turning from 
the phenomena of crystallization to the consideration of the 
causes producing them, it is apparent that the evidence of 
direct observation is the most important, and should be con¬ 
sidered first. The molten condition of volcanic lavas when 
they reach the surface of the earth testifies to the general 
condition of all igneous rocks previous to their solidification, 
and shows that we have to deal with the crystallization of 
molten magmas. 
The experiments of James Hall,* Gregory Watt,f Haubree,| 
Fouque, and Michel-Levy § upon the production of crystal¬ 
line rocks by artificial processes have demonstrated that cer¬ 
tain kinds of rocks can be produced by the simple cooling 
of fused magmas having the requisite chemical composition. 
The synthetical researches of Fouque and Michel-Levy 
are of special importance because of their extent and the iden¬ 
tity of the products they obtained to those occurring in 
nature. They succeeded in producing by purely dry fusion 
and gradual cooling at ordinary pressures a large number of 
the rock-making minerals, including anorthite, labradorite, 
oligoclase, nepheline, leucite, augite, enstatite, olivine, meli- 
lite, magnetite, and picotite. They also obtained certain 
basic rocks, as basalt, diabase, augite-andesite, nephelinite, 
leucitite, and lherzolite, and thereby proved that these rocks 
can be formed by the gradual cooling of magmas from a con¬ 
dition of purely igneous fusion at low pressures. 
* James Hall. “Experiments on whinstone and lava [1798].” Trans. 
Roy. Soc. Edinburgh, vol. 5, 1805, pp. 43-76. 
f Gregory Watt. “ Observations on basalt and on the transition from the 
vitreous to the stony texture which occurs in the gradual refrigeration of 
melted basalt, with some geological remarks.” Phil. Trans. Royal Soc., 
London, 1804, p. 179. 
t A. Daubree. Etudes synthetiques de geologie experimentale. Paris, 
1879, p. 517. 
§F. Fouque and Michel-Levy. Synthese des mineraux et des roches. 
