the Alps, which several of the ablest scholars
of Werner had determined to be transition, were ultimately ascertained,
by means of their fossil contents and position, to be members of the
Cretaceous, and even of the nummulitic or Eocene period. These strata
had, in fact, acquired the _transition_ texture from the influence of
causes which, since their deposition had modified their internal
arrangement.

_Texture and origin of Plutonic and metamorphic rocks_.--Among the most
singular of the changes superinduced on rocks, we have occasionally to
include the slaty texture, the divisional planes of which sometimes
intersect the true planes of stratification, and even pass directly
through imbedded fossils. If, then, the crystalline, the slaty, and
other modes of arrangement, once deemed characteristic of certain
periods in the history of the earth, have in reality been assumed by
fossiliferous rocks of different ages and at different times, we are
prepared to inquire whether the same may not be true of the most highly
crystalline state, such as that of gneiss, mica-schist, and statuary
marble. That the peculiar characteristics of such rocks are really due
to a variety of modifying causes has long been suspected by many
geologists, and the doctrine has gained ground of late, although a
considerable difference of opinion still prevails. According to the
original Neptunian theory, all the crystalline formations were
precipitated from a universal menstruum or chaotic fluid antecedently to
the creation of animals and plants, the unstratified granite having been
first thrown down so as to serve as a floor or foundation on which
gneiss and other stratified rocks might repose. Afterwards, when the
igneous origin of granite was no longer disputed, many conceived that a
thermal ocean enveloped the globe, at a time when the first-formed crust
of granite was cooling, but when it still retained much of its heat. The
hot waters of this ocean held in solution the ingredients of gneiss,
mica-schist, hornblende-schist, clay-slate, and marble, rocks which were
precipitated, one after the other, in a crystalline form. No fossils
could be inclosed in them, the high temperature of the fluid and the
quantity of mineral matter which it held in solution, rendering it unfit
for the support of organic beings.

It would be inconsistent with the plan of this work to enter here into a
detailed account of what I have elsewhere termed the _metamorphic