1G6 I'lie Avierican Geolo(/ist. March, 1897 
ui'Mlly have been tilled. By continiinl cooling, this magma, 
beginning at the walls, also crystallized out slowly and unin- 
terruptedly, often mixed with minerals which had been formed 
by special 'agents mineralisateurs' ; the conditions of such 
crystallization, proceeding from the walls of the htininn in- 
wards, must have been somewhat different from those of the 
former crystallization, which took place within the mass of the 
whole solidifying rock-matter, where the separate individuals 
must have crowded upon one another, etc.; hence the ever in- 
creasing size of grain, the zonal structure (conditioned by the 
crystallization from the walls inward), etc. If the magmatic 
silicate solution were not concentrated to such an extent that 
the Uiniitia were completely filled by its crystallization, first, 
open drusy cavities must have resulted, which finally through 
continued circulation might be filled in with minerals depos- 
ited from solutions at first still hot but later less and less hot. 
The filling up of the drusy cavities corresponds according to 
this interpretation pretty exactly to the complete vein forma- 
tion of the pegmatite veins which occur outside the normal- 
grained rock mass; the explanation throws light in both cases 
upon the continuous transition from the rock formed purely' 
by magmatic solidification to the final minerals of the' druses 
deposited from solutions not exactly magmatic (less concen- 
trated)." 
This statement certainly leaves much to be desired in the 
way of clearness, and we confess ourselves unable to gather 
from it with certainty the author's meaning. Considered 
simply as a suggestion or outline of the mode of formation of 
pockets, we should not care to criticise it. The references to 
more and less concentrated magmatic silicate solutions suggest 
the possible intervention or agency of water ; but in view of 
the facts that this is not explicitly stated and that anhydrous 
magmas are now generally regarded as true solutions, the idea 
of minimizing the aqueous influence is obvious. Whether 
Brogger should really be classed with the advocates of the ig- 
neous or the aqueo-igneous theory of pegmatite is, therefore, 
doubtful : and it has seemed best to us not to hazard a guess 
as to the possible hidden meaning of his language. 
Aqueo-igneous Theory. 
Although the igneous theory, even in its more modern forms, 
so obviously fails as a complete explanation of pegmatite, yet 
