606 The Genesis of Crystalline Rocks, (June, 
(1.) The plutonic hypothesis, which conceives the rocks in ques- 
tion to have been formed by the superficial cooling of a molten 
globe before the precipitation of water upon its surface. (2.) The ; 
volcanic hypothesis, which supposes them to be derived from 
igneous rocks, like lavas, coming from a liquid interior through — 
the primitive crust. (3.) The detrital or clastic hypothesis, | 
_which conceives them to have been made of the ruins of plutonic 
or volcanic rocks, more or less disintegrated or decayed 
rearranged by water, and subsequently modified by chemical 
changes. Similar alterations, through subsequent action of water, 
are also invoked by the advocates of the plutonic and volcanic 
hypotheses. (4.) The chaotic hypothesis, which supposes the 
elements of all these rocks to have been at one time dissolved of , 
suspended in the water of a primitive chaotic ocean. i 
The difficulties in the way of accepting any one of thes . 
hypotheses being pointed out, it was shown that the rocks i : 
question include a number of well-marked and lithology l 
distinct groups, each of great thickness, giving pome : 
successive depositions interrupted by foldings and erosions, a : 
extending over vast periods of eozoic time. The new ike a 
proposed by the writer to explain the origin of these rocks, aa 
the first three named, starts from the basis of a pe ng a 
lobe consolidating at the center, left, it is conceived, 4 Í 
a of basic silicates, which has yielded all the fixed aa 4 
of the earth’s crust. This layer formed the first land and j e ef 
of the primeval sea, the acid waters of which, permeating ] 
partially decomposing it, became thereby chemically ar a 
This last-cooled layer, mechanically disintegrated, satu as 
water, and heated by the central mass, was the sourr s the at 
springs holding in solution the silicates which built up 
cient gneisses and similar rocks. ; 4 by the history 
This hypothesis of their origin was illustrate d . 
of granitic veins, and by the derivation of quartz e 
and of zeolites (which are hydrated feldspars) ca 
action from basic rocks. All such deposits are ae 
the process which generated the gneissic rocks. pee by 
of their formation from materials brought to affords, it 
mineral springs from the primitive basic me eke explanatio® 
claimed, the elements of a complete and inte ig 
of the origin of the eozoic rocks, and was bret Se 
