168 The American Geohxjisf. March, isflT 
of pegmatitic \(A\\^ opening out into druses, and tinyJly the 
connection of these with vein-fillings wliich consist only of 
quartz, tourmaline and potash mica, or of quartz alone, can 
be explained, etc." Lehmann still farther emphasizes the role 
which water plays in the magma in holding that a high tem- 
perature is unnecessary to its formation and evolution. The 
increasing agency of water brings us next to Reyer,* who re- 
garded the pegmatites as excretions of the solidifying magma, 
representing the last stage of solidification where water was 
largely active, while Keilhau, Hausmann, and Daubree re- 
garded the pegmatites as mainly aqueous deposits, but genet- 
ically connected with granitic intrusions. 
Notwithstanding his belief in the igneous origin of peg- 
matites in general, Brogger accepts the aqueo-igneous theory 
for a not insignificant proportion of them. He saysf the peg- 
matites, although chiefly magmatically solidified veins, pass 
into the crack-fillings which succeed them in point of time 
and which are not in the main, or are not at all, deposited 
from true magmatic solutions. To this he adds in a foot- 
note, "Many large-grained veins of a pegmatitic structure 
have been formed principally by pneumatolitic (aqueo-igne- 
ous) processes, and not mainly by magmatic solidification," 
citing as examples the apatite-bearing basic veins and many 
occurrences of cassiterite, tourmaline, topaz, etc. Also that 
the muscovite granite pegmatite veins, cf»ntaining especially 
beryl, topaz, etc., and having as principal minerals microcline, 
oligoclase, albite, quartz, muscovite, are, in comparison with 
the ordinary granite pegmatite veins with which they fre- 
quently occur, of somewhat later formation, a slightly differ- 
ent magma, and to a larger extent of pneumatolitic formation. 
This review of opinion shows that while several previous 
writers have recognized the important and necessary agency 
of water in the formation of pegmatite, varying between heat 
as the chief agent with water cooperating (igneous jsrocesses), 
and water as the chief agent with heat cooperating (aqueous 
processes), Lehmann alone has given us a complete statement 
of the aqueo-igneous theory, or recognized the essential con- 
tinuity of the igneous and aqueous processes and the conse- 
*Theoretische Geologie, 101 (1888). 
tCanadian Record of Science, 6, 69. 
