164 The American Geolocjist. Manii, i897 
to this question is to be found in the characters of granite — 
a fine and even-grained rock of remarkably uniform composi- 
tion and devoid of pockets. This absolute lack of agreement 
in the fundamental characters seems to render a more detailed 
comparison superfluous. It is thus obvious that the igneous 
theory also, although accounting satisfactorily for the order 
of cr3rstallization in pegmatite, broken crystals of tourmaline 
and beryl, parallel orientation of inclusions, etc., requires 
important modification, and especially a larger intervention 
of water; for it does not appear that the variation of any other 
factor, such as pressure or temperature, would meet the ne- 
cessities of the case. 
Brogger. however, among recent writers, seems disposed to 
minimize the influence of water: and in the differentiation of 
pegmatite from normal granite to allow it practically no part 
whatever. He says* "the principal requirement for the solid- 
itication of deep-seated magmas to holocrystalline plutonic 
rocks, seems, therefore, to consist in a sufficiently slow cool- 
ing of the water-bearing magma, under a pressure of super- 
imposed matter great enough to prevent the water separated 
out by crystallization from freely escaping to the surface, and 
compelling it by a pressure exerted from above to pass into 
the wall-rock (contact metamorphism ).'' Although so clearly 
recognizing the presence of water, and using it to account for 
certain contact phenomena, he does not, apparently, regard it 
as in any wa^^ essential to magmatic differentiation, either 
chemical or textural, but treats the magma, virtually, as if it 
were anhydrous througliout its entire histor}' ; and yet he 
repeatedly invokes the aid of certain "agents miiieralisateurs," 
which are nowhere more explicitly designated or described. 
His non-utilization of the water in the magma obliges him to 
refer the gigantic cryst:»llization and irregular composition so 
characteristic of pegmatite wholly to the slowness with which 
it has cooled and solidified. He saysf "both when they (the 
pegmatites) occur in the main mass of the allied eruptive rock 
(parent plutonic), and when they occur in the neighborhood 
— and one of the two is always the case — we may assume that 
the rock surrounding the vein-stone (pegmatite) was first 
*L. c, 45. 
tL. c., 67. 
