12 . T. STERRY HUNT ON THE GENETIC 
§ 13. The crenitic hypothesis advanced by the present writer in the essay already cited, 
to explain the aqueous origin of the mineral species which make up alike the granites and 
the crystalline stratified rocks, supposes that from an early period watery solutions analo- 
gous to those which, in later times, have given rise to zeolitic and pectolitic minerals, played 
an important part in the chemistry of the earth. The double silicates of alumina and lime 
or alkalies, then dissolved, are conceived to have been the source not only of the feldspars 
and the zeolites, but of prehnite, epidote, garnet, muscovitic micas, and tourmalines, and, by 
their reactions with magnesian and ferrous solutions, of the chlorites and the highly proto- 
basic micas. At the same time the dissolved protoxyd-silicates not only gave rise to species 
like pectolite and apophyllite, but by similar reactions, to pyroxene, amphibole, chrysolite, 
serpentine, talc, sepiolite, and glauconite, and, by decomposition through carbonic dioxyd, 
to carbonate of lime. In both cases the solutions, like those in later zeolite-bearing rocks, 
carried free silica and iron-oxyd, which were deposited as quartz and magnetite and hema- 
tite. These silicated solutions, according to this hypothesis, resulted primarily from the 
action of permeating waters at high temperatures, under pressure, upon the universal 
stratum of basic plutonic rock, and secondarily from their action upon the displaced por- 
tions of the stratum, which, in a more or less modified form, have appeared in all geological 
periods as erupted basic rocks. These, in their secreted minerals, show us in later times, 
and on asmaller scale, the process which, in previous ages, built up great masses of indige- 
nous and endogenous crystalline rocks. To what extent these deposits, more or less con- 
cretionary in their origin and their arrangement, were laid down horizontally, and to what 
extent in inclined or vertical layers, as in many veinstones, is a question which will be 
discussed farther on in this essay. 
§ 14. Having thus briefly restated the crenitic hypothesis so far as it is related to the 
classes of rocks already noticed, we have to consider in the next place the question of 
exoplutonic or eruptive rocks. It will be remembered that the existence of such rocks, 
having an igneous origin, was not admitted by the Wernerians, who conceived not only 
all endogenous rocks, but also all exotic masses, except modern lavas, to be of aqueous 
origin. By the earlier Huttonians, who understood better the geological importance of 
the eruptive rocks, these were looked upon as results of the fusion of deeply buried 
detrital materials, themselves derived from similar rocks of higher antiquity. The hypo- 
thesis of great chemical changes to explain the genesis of many crystalline rocks from 
such material, by what was comprehensively designated as “ metamorphism,” and generally 
involved a supposed metasomatic process, was devised at a later day by the disciples of 
Hutton. Haidinger and Bischof may be looked upon as the originators of that view of 
metasomatic changes in rock-masses by aqueous action which, from its supposed analogy 
with the phenomena giving rise to what are called “ pseudomorphous shapes ” or “ pseudo- 
crystals,” has been infelicitously described as “ pseudomorphism on a broad scale.” 
§ 15. The stratiform arrangement, which extends to the intimate structure of crystal- 
line masses such as gneisses and mica-schists, is by endoplutonists supposed to be due to 
movements in an imperfectly homogeneous semi-fluid material, dependent on unequal 
cooling and the rotation of the globe, and to be analogous to the banded structure apparent 
in lavas and furnace-slags. In the exop]utonic hypothesis, on the contrary, it is maintained 
that the internal movements in such material, when forced outwards and upwards through 
the earth’s superficial crust, have given to the masses that laminated structure and that 
