149 
felspars in magmas! has expressed a somewhat different opinion. 
He supposes that the felspar of which the chemical composi- 
tion has been given) above has formed as a homogeneous crystal 
of potash-felspar containing the highest admixture possible of 
albite-silicate (according to his theory about 28 per cent.), and 
that the perthitic structure has originated by recrystallization 
when the solid crystal adjusted itself to another state of equi- 
librium at a lower temperature. It deserves notice, therefore, 
that the structural feature mentioned above is not the only fact 
telling against the view of Professor Voer. Thus, the micro- 
scopical examination of the rock indicates the presence of all 
gradations connecting the perthites in which albite dominates 
with those containing prevalent microcline; and the naujaite 
itself with its perthitic felspars is connected by gradual transi- 
tions with the lujavrites in which microcline and albite occur 
in separate crystals of widely varying relative amounts *. 
1 J. H. L. Voor, Physikalisch-chemische Gesetze der Krystallisationsfolge 
in Eruptivgesteinen. Tschermak’s Mineralogische und Petrographische 
Mitteilungen XXIV, p. 533 (1906). 
Another hypothesis set forth by Professor Vocr (loc. cit р. 522) and 
relating to the same question, viz. that the cryptoperthites of certain 
augite-syenites (larvikites) represent the eutectic mixture of soda- and 
potash-felspar also seems open to some doubt. As a matter of fact 
the augite-syenites in question in many localities occur in connection 
with nepheline-syenites containing perthitic alkali-felspars of a chemical 
composition which differs considerably from that of the eryptoperthites, 
and for geological reasons it seems very unlikely, if not impossible, that 
the felspars of the augite-syenite have crystallized at a lower temperature 
than the other felspars. At Ilimausak the naujaite-pegmatite has 
evidently erystallized at a lower temperature than the naujaite itself, 
and this in turn has crystallized at a lower temperature than the 
augite-syenite which is of the Larvik type. Accordingly it might be 
expected that the eutectic alkali-felspar was to be found in the pegma- 
tite rather than in the augite-syenite. But in the hypothesis of Profes- 
sor Vocr the reverse is assumed: the pegmatitic felspar mentioned 
above is quoted as an instance of an originally homogeneous soda-bear- 
ing potash-felspar, and the felspar of the augite-syenite is interpreted 
as an eutectic intergrowth. To the present writer the assumption 
seems more likely that the augite-syenitic cryptoperthites in most cases 
have erystallized at a relatively high temperature as originally homo- 
to 
