LIBRARY 
OF THE 
UNIVERSITY of ILLINOIS. 
THE 
AMERICAN GEOLOGIST. 
Vol. XIX. MARCH, 1897. No. 3 
ORIGIN OF PEGMATITE. 
By W. O. Crosby* and M. L. Fuller, Boston, Mass. 
[From the Mass. Inst. Technology Quarterly, vol. ix, pp. 326-856, Dec, 1896.] 
Introduction. 
The history of geology is replete with theories of pegma- 
tite, or giant granite — manifold modifications of the agenc}' 
of water and heat; and this diversity of opinion finds a ready 
explanation in the fact that in no other class of rocks do we 
find such a perfect combination of aqueous and igneous char- 
acters. Although the intimate association and evident close 
connection of pegmatite with undoubted lalutonic rocks, and 
*Nearly three years ago (December, 1893) I read a paper on the "Ori- 
gin of Pegmatite" before the Geological Society of America, a brief ab- 
.stract of which appeared in the American Geologist for March, 1894. 
(See, also, Mass. Inst. Technology Quarterly, vol. 7, pp. .30-81.) In that 
paper I developed in outhne the modification of Lehmann's aqvieo-igneous 
theory of pegmc;tite, which is more completely elaborated and substan- 
tiated in the present contribution: but its publication was deferred, 
awaiting an opportunity to more thoroughly test the theory in the field. 
In the summer of 1895 i was able to spend a few days in the pegmatite 
district of Grafton and Sullivan counties, in southwestern New Hamp- 
shire, and later in the year Mr. Fuller, a student in the Geological De- 
partment of the Massachusetts Institutes of Technology, undertook, 
under my direction, a more extended and detailed study of the pegma- 
tites of that region, basing thereon his thesis for graduation the follow- 
ing June. Mr. Fuller's investigation has materially modified and 
strengthened the aqueo-igneoue theory, and hence this joint production. 
W. O. Ckosbv. 
