is no longer capable of being applied when we come to the study of widely
distant regions. This important conclusion led up to the further
generalisation that each great geological period has exhibited a
geographical distribution of the forms of animal and vegetable life,
comparable to that which prevails in the existing fauna and flora. To those
who are familiar with the extent to which the doctrine of universal
formations has affected geological thought and speculation, both long
before and since the time that Darwin wrote, the importance of this new
standpoint to which he was able to attain will be sufficiently apparent.
Like the idea of the extreme imperfection of the Geological Record, the
doctrine of LOCAL geological formations is found permeating and moulding
all the palaeontological reasonings of his great work.

In one of Darwin's letters, written while he was in South America, there is
a passage we have already quoted, in which he expresses his inability to
decide between the rival claims upon his attention of "the old crystalline
group of rocks," and "the softer fossiliferous beds" respectively. The
sixth chapter of the work before us, entitled "Plutonic and Metamorphic
Rocks--Cleavage and Foliation," contains a brief summary of a series of
observations and reasonings upon these crystalline rocks, which are, we
believe, calculated to effect a revolution in geological science, and--
though their value and importance have long been overlooked--are likely to
entitle Darwin in the future to a position among geologists, scarcely, if
at all, inferior to that which he already occupies among biologists.

Darwin's studies of the great rock-masses of the Andes convinced him of the
close relations between the granitic or Plutonic rocks, and those which
were undoubtedly poured forth as lavas. Upon his return, he set to work,
with the aid of Professor Miller, to make a careful study of the minerals
composing the granites and those which occur in the lavas, and he was able