176 The Aniericnn Geologist. Marth, 1897 
tion in the parent plutonic, or in the surrounding formations. 
Second, apophyses of the normal granite magma maj'^ invade 
highly heated, water-bearing formations, such as the schists, 
and experience the necessary hydration for conversion into 
pegmatite magma through the absorption of this extraneous 
water. The high temperature of the wall-rock is essential, as 
previously noted, to prevent the chilling and crystallization 
of the magma before the absorption of water can take place. 
It cannot be argued that this principle would lead to a per- 
ipheral development of pegmatite in the main bodies of gran- 
ite, for while tiie volume of water-bearing wall-rock per unit 
of surface of the body of magma would not be increased, the 
volume of magma through which the water would be diffused 
as fast as absorbed would be enormously greater and no ex- 
ceptional or marked degree of hydration could result. That 
the wall-rock must have been highly heated, contrary to Leh- 
mann's view, is reasonably' certain from the absence in both 
the granites and pegmatite of the normal gradation in tex- 
ture due to the chilling action of the walls. On the other 
hand, this high temperature probably would not tend to expel 
the water from tlie inclosing formations, and thus prevent 
them from contributing water to the invading magmas; for 
the w^ell-known experiments of Daubree and Poiseuille indi- 
cate that within certain limits, at least, the heat favors rather 
than hinders the downward progress of the water in the 
earth's crust ; and it appears to us very probable that the ab- 
sorption of water b}" deep-seated magmas is another cause 
operating to the same end. It can hardly be doubted that the 
temperature was well above the critical point for water, and 
hence the hydration of the magma really means the absorp- 
tion of superheated aqueous vapor under enormous pressure. 
This extension of the pegmatite theory overcomes the obvious 
difficulty as to the extensive extravasation of pegmatite mag- 
ma evolved or originating deep down in a great boss of solid- 
ified granite; and apophyses of normal granite accompanying 
pegmatite may reasonably be referred to a somewhat earlier 
period, when the thermal conditions were still unfavorable to 
aqueous absorption. 
Pegmatite magma may not only be assumed to be more 
liquid than that of normal granite, but to solidify less prompt- 
