DESCRIPTION OF ROCKS AND ANALYSES 35 
attention to the possibility of explaining the genesis of the two 
rocks differing in such a degree but closely connected one with 
another in space and probably in time too, by progress of cristalli- 
sation during the cooling process after the sheme given by Bowen 
for the silicate rocks in general." The content of mafic minerals, 
being common and almost of the same kind in both rocks, except 
small quantities of accessories, can be neglected in the following 
discussion. 
In decreasing the temperature the degree of dissociation of the 
magma-components diminishes and the cristallisation process can 
be derived from the ternary system: quartz (SiO,) — alumosilicate 
of alkalies lowest in silica (i. e. Na(K)AISiO, [nephelite]) — a hypo- 
thetical alumosilicate of lime lowest in silica (i. e. CaAl,SiO,). 
Sid, 
Alkalifeldspars RL 
N Anorthite 
Leucile-groun 
NaVALSi 0, CoALSiO, 
IN ae l tle-group) 
Kies. 
Although the pecularities of this system are not yet known, the 
way of crystallisation of a solution, whose composition lies near 
the base of fig. 1 in x, can in some measure be foreseen. In an 
early stage of crystallisation the lenads will begin to separate, but 
after the bulk of mafic minerals crystallised out and the rest solution 
acidilied, the lenads become instable and due to resorption; the 
I N. L. Bowen, in Journal of Geology, Suppl. to vol. 23. 1915. 
