116 
IDDINGS. 
point and brings into prominence those theories of magmas 
which consider them to be alloys or solutions of silicate 
molecules capable of becoming supersaturated with one or 
another of these compounds. It considers the effect of 
changes of temperature and pressure on the degree of satura¬ 
tion, and also the influence of absorbed gases on crystalliza¬ 
tion. He considers it most probable that the different sili¬ 
cates remain as such or as similar but constant compounds 
in the molten magma, by which is meant only the funda¬ 
mental compounds (“ Grand verbindungen”). He further 
assumes that the same minerals always crystallize from 
similar magmas. 
It is to be remarked that however important these con¬ 
ceptions of the crystallization of igneous magmas have 
proved in their application to the broader questions affect¬ 
ing the origin and relationships of igneous rocks, Lagorio 
completely failed to appreciate it; for in the very para¬ 
graph in which he applies the principle discovered by Soret 
to the explanation of the separation of the material of cer¬ 
tain dikes he makes use of Bunsen’s hypothetical pyroxenic 
and trachytic magmas, and states in a foot-note that he con¬ 
siders Bunsen’s hypothesis for the origin of different lavas 
as not having been done away with by any means. 
Soret observed that if different parts of a solution of a 
salt be maintained at different temperatures there will be a 
concentration of salt in the colder part—a principle in¬ 
volving differentiation, the antithesis of Bunsen’s synthetical 
theory. 
The application of this principle to igneous magmas in 
general was subsequently suggested by Teall,* in 1888, in 
his work on “ British Petrography.” In discussing the crys¬ 
tallization of igneous rocks he quotes Lagorio’s explanation 
of the differences between the center and walls of certain 
dikes, and adds, “ Soret’s principle may also be applicable to 
plutonic rocks. Homogeneous molten masses may become 
heterogeneous by diffusion of certain constituents during 
* Teall (J. J. H.) British Petrography. *8°. London, 1888, p. 403. 
