Origin of Pegrnatite. — Croah]) amJ Fuller. 169 
quent complete blending of fuHion and solution, and their 
products — the igneous and aqueous rocks. The present paper 
may be regarded, therefore, as based upon Lehmann's work — 
a restatement of his views, with more complete elaboration 
and illustration in certain directions. 
All lavas appear to be more or less hydrated -it the time of 
their extrusion; and, however much opinions may differ con- 
cerning the source of the water and its original relations to 
the magma, it is generally conceded that at the moment of 
eruption they are very intimately united, and that the former 
increases the liquidity and the eruptive energy of the latter. 
Water is very thoroughly diffused through the earth's crust; 
and it has probably penetrated to so great a depth as to war- 
rant the conclusion that all the so-called igneous rocks now 
exposed to our observation are in some degree the products of 
aqueo-igneous fusion. It is unnecessary. however,to insist upon 
this broad generalization, for, although it may be questioned 
for some of the plutonic rocks, it is very generally conceded 
to be true for those with which we now have to do — the acid 
plutonics or the granites. 
The order of crystallization of the component minerals, and 
the fact that the quartz, which has been in every instance the 
last mineral to crystallize, is usually crowded with aqueous 
inclusions, leave no room to doubt that water was present and 
played an important part in the formation of granite. It is 
<iuite unnecessary to raise here the question as to whether or 
not the granites are metamorphosed sediments; for those who 
would answer in the negative must, apparently, concede that 
there is a h3alrated zone of the primitive igneous crust be- 
neath the oldest sediments. In fact, the hydration of the 
original or still unstratitied igneous crust to a great depth 
below the oldest sedimentary rocks appears to the writers a 
peculiarly safe assumption, for we have to do here with a 
portion of the primitive crust which formed the immediate 
Hoor of the primitive ocean. 
Assuming, then, without farther argument, that the gran- 
ites have been formed in the presence of water, it may be 
noted that the number, minuteness, and universal presence of 
the liquid inclusions indicate that, as in modern lavas, the 
water was very intimately combined with the granite magma. 
