110 LHE JfOORNAL OF GEOLOGY. 
quartz, silver-gray muscovite, and biotite. The spheroids were formed 
in the following way : : 
During the eruption of the granitic magma fragments of a foreign 
granitic rock were surrounded by the granitic magma: The solid 
granite may have been “foreign” or it may have been from the 
already solidified portions of the magma. Resorption began and 
continued until the magma was supersaturated and the temperature 
lowered to a point where a new crystallization could begin. 
The included granite consisted of orthoclase phenocrysts in a fine- 
grained groundmass which was moré readily dissolvable than the com- 
pact feldspar. Though the phenocrysts did not remain entirely 
unattacked they were not completely resorbed, and an outer mixed 
zone was formed between them and the individualized magma. The 
subsequent crystallization took place in the mixed zone under the 
orienting influence of the feldspar. At the moment when crystalliza- 
tion reached the outer zone of influence the whole magma crystallized 
to a panidiomorphic-granular mixture. 
In this case, as in the first, the character of the zircons proved a 
valuable aid in the interpretation of the varioles’ genesis. The main 
mass and the core carried zircons of different habits, while the shell 
of the variole carried both types. 
4. Variolititic granite from Ghistorrai near Fonni, Sardinia. 
As in the cases above cited fragments of different rocks were sur- 
rounded and taken into the granitic magma, where their constituents 
were disassociated and in part resorbed. From this simple proposition it 
would seem that the rocks under consideration would be other than rare ; 
there are, however, certain conditions essential to “kugelbildung.” 
“The inclusions must be concentrated within the predominant 
rock magma to the smallest possible space so that between them a 
relatively small amount of magma remains included. ‘The enclosing 
part of the magma then enters into an exchange with the inclusion, 
and there is established corrosion, resorption, and recrystallization, 
though the magma may circulate very slowly between them, ¢. g., bring- 
ing in from without and distributing from within. In consequence 
of this action the mixed zone supersaturated with material from the 
inclusion may remain stationary a long time. Under such circum- 
stances a rapid crystallization tending towards a radial structure may 
set in more readily than in homogeneous granite where the crystalliz- 
ing conditions naturally must be distributed equally.” P. 129. 
