162 The American Geologist. March, 1897 
AqUKOUS TlIEOUIES. 
All subterranean aqueous deposits may be referred to three 
classes: veins, impregnations, and substitution deposits.* 
The second and third classes may safely be set aside at once 
as incapal)le of throwing any light upon the origin of pegma- 
tite; unless, indeed, the solution and absorption of a body of 
schist by molten magma be regarded n?-, a mode of substitu- 
tion. It is sufficient for our present purpose to recognize the 
two main types of veins: (1) endogenous veins formed chiefly 
by ascending solutions in fissures or cavities; (2) exogenous 
veins, formed chiefly bj^ lateral secretion in rocks devoid of 
sensible fissures or cavities. The characters of the endogen- 
ous or fissure veins are well known, the most significant per- 
haps, being the banding or crustification, comb-structure and 
pockets. The exogenous or segregation veins are especially 
characterized by their homogeneity of composition and struc- 
ture and the absence of pockets. 
The view that pegmatite masses are, in origin, akin to 
mineral veins, originally proposed by Saussure, has in recent 
years been most positively asserted and strongly defended by 
T. Sterry Hunt. He heldf that the pegmatites have been 
formed by the successive deposition of mineral matter from 
solution, usuall}^ in open fissures; and in the development of 
the crenitic hypothesis;|; he states that "the gneisses and 
bedded granites are to granitic veins (pegmatite) what beds 
of chemically deposited limestone and travertine are to calca- 
reous veins." 
In reviewing the characters of pegmatite, a goodly portion 
are found to be common to one or the other of the two types- of 
veins noted above; and to admit of explanation, therefore, by 
the purely aqueous theories. Among these are the following: 
(1) rare minerals; (2) coarse crystallization; (3) banding 
and comb-structure, with tourmalines, etc., normal to the 
walls; (4) inclusions of water in quartz, etc.; (5) pockets 
and druses. On the other hand, vein formation does not sat- 
isfactorily explain : (1) the order of crystallization, except in 
pockets; (2) completely idiomorphic crystals; (3) the graph- 
*Technology Quarterly, 7, 27-48. 
fNotes ou Granitic Rocks, Amer. Jour. Sci., Ill, 2, 89. 
JMiueral Physiology and Physiography, 1886, 133. 
