104 
IDDINGS. 
although the original bath presented the same composi¬ 
tion.”* 
In the appendix already mentioned he refers more defi¬ 
nitely to “ the products of the phenomena of liquation which 
have operated within the liquid or viscous mass and have 
separated it into different compounds.”f 
This appears to have been the first comparison of rock 
magmas to alloys, and the conception of their separation 
into bodies of different composition processes of liqua¬ 
tion, though applied to only a limited range of phenomena. 
Durocher also imagined that the access of sea water to 
molten magmas affects their chemical composition, rendering 
them more alkaline. He also argues that because of the in¬ 
dependent action of neighboring volcanic vents, and of the 
irregularity and often weakness of their action, it does not 
seem likely that these vents connect directly with the gen¬ 
eral reservoir of magma, but only with secondary bodies in 
branching fissures (“ foyers secondaires ”). They are thus 
in a measure local. 
In 1858 Von Cotta J advanced the theory that the solid 
crust of the earth consisted of highly silicious substances, and 
that the fused portion beneath had about the composition of 
the most basic rocks, and that the variations in the compo¬ 
sition of eruptive rocks were due to the variable amount of 
the solid silicious crust which was taken up by the basic 
magma during its passage toward the surface of the earth. 
In 1861 Justus Roth § explained the various mineralogical 
*Op. cit., p. 220: 
“ Les magmas qui ont produit les roch.es ignees sont comparables a des 
bains contenant 4 l’etat de fusion plusienx metaux, et qui, en se figeant, 
se partagent en des alliages divers, suivant les circonstances de leur solid¬ 
ification, lors m£me que le bain primitif offrait la meme composition.” 
t Op. cit., p. 677 : 
“ Les produits de phenom&nes de liquation qui se sont operes au sein 
de la masse liquide ou p&teuse, et Font partagee en des composes difie- 
rentes.” 
t Von Cotta (B.) Geologische Fragen. 8°. Freiberg, 1858, p. 78. 
g Both (J.) Die Gesteins-analysen in tabellarischer iibersicht und mit 
kritischen Erlauterungen. 4°. Berlin, 1861, p. xix. 
