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102 IDDINGS. 
“ If it be well founded, it will enable us to account for the 
gradual changes in one connected igneous mass, as also for 
the veins and patches of different character sometimes to be 
found occurring very abruptly in such masses, independently 
of the supposition of a subsequent intrusion of one igneous 
rock through the body of another. This would often relieve 
us of a difficulty where the veins are confined to the igneous 
rock and do not penetrate the adjacent aqueous rocks. We 
might then look upon such veins as veins of segregation, 
occurring probably at the time of the contraction consequent 
upon the mass of the rock passing from a molten to a solid 
state or from a pasty to a crystalline state while yet some 
parts of it remained fluid.” 
In this hypothesis there is the partial solidification of a 
molten magma at some depth and the squeezing up of the 
unconsolidated portion, together with the suggestion that 
the molten magma gathered up new material from the rocks 
through which it passed. 
In the same year, 1857, Durocher published his “ Essay 
on Comparative Petrology,” * in which he enunciated the 
view, which he claims f was original with himself, that all 
rocks, modern and ancient, have been produced simply by 
two magmas which coexist beneath the solid crust of the 
earth and occupy a definite position. 
These magmas have not changed in themselves during 
long ages, and differ from one another by distinct characters. 
One he calls the “ magma acid ” or “ siliceux,” and the other 
the “ magma basique.” 
He observes that there are greater chemical differences 
between different kinds of granite than between granite and 
trachyte or pumice; therefore one may conclude that “ for 
* Durocher (J.) Essai de Petrologie Comparee, ou recherches surla 
composition chimique et mineralogique des roches ignees, sur les phe- 
nomfines de leur emission et sur leur classification. Ann. des Mines. 8°. 
Paris, 1857, vol. 11, pp. 217-259. 
t Appendice au Memoire intitule Essai de Petrologie Comparee, etc., 
p. 677, same volume. 
