materials, at a great depth, are passing from a solid to a fluid state, and then
reconsolidating, so as to acquire a new texture.

As all the crystalline rocks may, in some respects, be viewed as belonging to
one great family, whether they be stratified or unstratified, metamorphic or
Plutonic, it will often be convenient to speak of them by one common name. It
being now ascertained, as above stated, that they are of very different ages,
sometimes newer than the strata called secondary, the terms primitive and
primary which were formerly used for the whole must be abandoned, as they would
imply a manifest contradiction. It is indispensable, therefore, to find a new
name, one which must not be of chronological import, and must express, on the
one hand, some peculiarity equally attributable to granite and gneiss (to the
Plutonic as well as the ALTERED rocks), and, on the other, must have reference
to characters in which those rocks differ, both from the volcanic and from the
UNALTERED sedimentary strata. I proposed in the Principles of Geology (first
edition volume 3) the term "hypogene" for this purpose, derived from upo, under,
and ginomai, to be, or to be born; a word implying the theory that granite,
gneiss, and the other crystalline formations are alike NETHERFORMED rocks, or
rocks which have not assumed their present form and structure at the surface.
They occupy the lowest place in the order of superposition. Even in regions such
as the Alps, where some masses of granite and gneiss can be shown to be of
comparatively modern date, belonging, for example, to the period hereafter to be
described as tertiary, they are still UNDERLYING rocks. They never repose on the
volcanic or trappean formations, nor on strata containing organic remains. They
are HYPOGENE, as "being under" all the rest.

From what has now been said, the reader will understand that each of the four
great classes of rocks may be studied under two distinct points of view; first,
they may be studied simply as mineral masses deriving their origin from
particular causes, and having a certain composition, form, and position in the