CRYSTALLIZATION OF IGNEOUS ROCKS. 
95 
volcanic rocks or in the coarsely crystalline ones; nor have 
they produced the feldspars in those isomorphous series so 
common to eruptive rocks. In this respect they have only 
suggested the possible necessity of a mineralizing agent, and 
have indicated the lines upon which further research should 
be made. 
Conclusions Based upon Analogy .—Leaving the firm ground 
of direct experimentation for the uncertain footing of specu¬ 
lation, we come to the consideration of the probable nature 
of molten rock magmas. 
In 1861 Bunsen pointed out the correspondence between 
rock magmas and solutions of salts. Calling attention to 
the fact that the order of crystallization of the essential min¬ 
erals in granite was not in accord with their fusibility, and 
that their order of separation from the magma upon its 
cooling was not that which should be expected if they existed 
in it simply as fused substances, it corresponded to what 
would happen if they were in solution in one another and 
obeyed the laws governing the solution of salts. He remarks 
that “no chemist would think of assuming that a solution 
ceases to be a solution when it is heated to 200, 300, 400 de¬ 
grees, or when it reaches a temperature at which it begins 
to glow, or to be a molten fluid. Thus, for example, he would 
not think of assuming that a mixture of ice and crystallized 
calcium chloride, which has become fluid, is indeed a solu¬ 
tion, but that a fluid mixture of quartz and feldspar is not, 
because it becomes fluid at a red heat. No one can longer 
entertain the slightest doubt that that which holds good for 
solutions at lower temperatures must also hold good for solu¬ 
tions at higher temperatures.”* 
Schottf considered glasses as supersaturated solutions anal¬ 
ogous to salt solutions, and Lagorio,J in 1887, assumes that 
* R. Bunsen. Zeitschr. deutsch. geol. Gesell., vol. 13, 1861, p. 62. 
t Schott. Poggendorff, Annalen, vol. 154, p. 422. 
J A. Lagorio. “ Ueber die Natur der Glasbasis, sowie der Krystallisa- 
tionsvorgange im eruptiven Magma.” Tschermak’s min. pet. Mitth., vol. 
8, 1887, p. 437. 
