16 T. STERRY HUNT ON THE GENETIC 
both of which these two classes of rocks have come directly from a primitive fused mass, 
which was either simple or had become complex through differentiation. The Huttonian 
school also, which teaches that eruptive rocks, in many if not in all cases, were originally 
sediments, which, as a result of profound alteration, have lost their bedded structure, 
arrives, by a different route, at a conclusion not unlike that of the plutonists ; namely, 
that the differences between stratified and unstratified rocks are due solely to superin- 
duced structure and geognostic relations. Those who, for the most part unfamiliar with 
any other view, acquiesce in the metamorphic hypothesis of Hutton and his followers, 
now so popular with a school of writers on geology, are scarcely prepared, without far- 
ther study, to criticise intelligently either the plutonic or the crenitic hypothesis of the 
origin of crystalline rocks. The latter, as set forth in a previous easy, and concisely 
resumed in § 13 of the present, supposes that the source of all crystalline rocks is to be 
sought in a previously solidified primary plutonic material. The elements of these rocks 
have been derived, in part indirectly, by aqueous solution, and in part directly from this 
original mass, more or less profoundly altered alike by previous aqueous action, and by 
differentiation through crystallization and eliquation. By this hypothesis, as we have 
elsewhere attempted to show, we may hope to lay the foundation of a rational geogeny 
and geognosy. 
§ 23. We have already, in the preceding essay, considered at some length the views 
of those who, noting the existence of predominant types of crystalline rocks, have sought 
to explain their origin by supposing the presence beneath the earth’s solid crust of two 
distinct layers of molten rock: an upper, lighter, and more viscous siliceous or so-called 
acidic stratum, the material of trachytes, granites, and gneiss; and a lower, heavier, and 
more fluid basic layer, the source of doleritic and basaltic rocks,—a view which was put 
forth by John Phillips,’ defended by Bunsen, and elaborated and more definitely formu- 
lated by Durocher. To this are opposed the modified view, by Von Waltershausen, of a 
eradual passage downward in a liquid mass from a more acidic to a more basic portion, 
and the entirely distinct view held and defended by the present writer as the basis of the 
crenitic hypothesis. According to this, the plutonic underworld, so far as it intervenes 
directly in geologic phenomena, is an essentially homogeneous basic rock, not in a state 
of simple and original igneous fusion, but solidified, and subsequently impregnated with 
water, which communicates a certain plasticity to the highly heated mass, and, moreover, 
dissolves and removes therefrom the materials of the trachytic annd granitic rocks,—which 
are thus primarily of aqueous origin. 
§ 24. This process implies secular changes in the composition of the plutonic stra- 
tum, which are moreover local, since the conditions of solution and upward percolation 

1 John Phillips, Manual of Geology (1855), p. 556, after distinguishing between rocks like granite and trachyte, 
containing quartz and trisilicates (orthoclase and albite), and rocks with more basic silicates, such as labradorite, 
pyroxene and chrysolite, suggests “the probability that granite appears among the oldest of the igneous family 
because of the gradual cooling of the internal fluid mass, which, bringing into action the unequal relation to heat 
of the silicates and trisilicates, separated these groups in zones. The former (usually more complicated) mixture 
might remain liquid, while the latter (usually less complicated) separated themselves in a solid state. On this 
supposition the trisilicated zone, being of less specific gravity, would be uppermost. It would be first consolidated, 
and might receive a coating of strata, while the silicated mass remained liquid below.” On this hypothesis, he 
adds: “The trachytic lava of one active volcano, and the doleritic lava of another, would seem to indicate the 
stage to which, in those places respectively, the volcanic process had arrived.” 
a 
