Geological Observations on South America | Page 6

is purely geological. I
said to my brother, 'You will of course read it,' and his answer was,
'Upon my life, I would sooner even buy it.'"
In spite of these disparaging remarks, however, we are strongly
inclined to believe that this book, despised by its author, and neglected
by his contemporaries, will in the end be admitted to be one of
Darwin's chief titles to fame. It is, perhaps, an unfortunate circumstance
that the great success which he attained in biology by the publication of
the "Origin of Species" has, to some extent, overshadowed the fact that
Darwin's claims as a geologist, are of the very highest order. It is not
too much to say that, had Darwin not been a geologist, the "Origin of
Species" could never have been written by him. But apart from those
geological questions, which have an important bearing on biological
thought and speculation, such as the proofs of imperfection in the
geological record, the relations of the later tertiary faunas to the recent
ones in the same areas, and the apparent intermingling of types
belonging to distant geological epochs, when we study the
palaeontology of remote districts,--there are other purely geological
problems, upon which the contributions made by Darwin are of the
very highest value. I believe that the verdict of the historians of science
will be that if Darwin had not taken a foremost place among the
biologists of this century, his position as a geologist would have been
an almost equally commanding one.
But in the case of Darwin's principal geological work--that relating to
the origin of the crystalline schists,--geologists were not at the time
prepared to receive his revolutionary teachings. The influence of
powerful authority was long exercised, indeed, to stifle his teaching,
and only now, when this unfortunate opposition has disappeared, is the
true nature and importance of Darwin's purely geological work
beginning to be recognised.

The two first chapters of the "Geological Observations on South
America," deal with the proofs which exist of great, but frequently
interrupted, movements of elevation during very recent geological
times. In connection with this subject, Darwin's particular attention was
directed to the relations between the great earthquakes of South
America--of some of which he had impressive experience--and the
permanent changes of elevation which were taking place. He was much
struck by the rapidity with which the evidence of such great earth
movements is frequently obliterated; and especially with the
remarkable way in which the action of rain-water, percolating through
deposits on the earth's surface, removes all traces of shells and other
calcareous organisms. It was these considerations which were the
parents of the generalisation that a palaeontological record can only be
preserved during those periods in which long-continued slow
subsidence is going on. This in turn, led to the still wider and more
suggestive conclusion that the geological record as a whole is, and
never can be more than, a series of more or less isolated fragments. The
recognition of this important fact constitutes the keystone to any theory
of evolution which seeks to find a basis in the actual study of the types
of life that have formerly inhabited our globe.
In his third chapter, Darwin gives a number of interesting facts,
collected during his visits to the plains and valleys of Chili, which bear
on the question of the origin of saliferous deposits--the accumulation of
salt, gypsum, and nitrate of soda. This is a problem that has excited
much discussion among geologists, and which, in spite of many
valuable observations, still remains to a great extent very obscure.
Among the important considerations insisted upon by Darwin is that
relating to the absence of marine shells in beds associated with such
deposits. He justly argues that if the strata were formed in shallow
waters, and then exposed by upheaval to subaerial action, all shells and
other calcareous organisms would be removed by solution.
Following Lyell's method, Darwin proceeds from the study of deposits
now being accumulated on the earth's surface, to those which have been
formed during the more recent periods of the geological history.

His account of the great Pampean formation, with its wonderful
mammalian remains--Mastodon, Toxodon, Scelidotherium,
Macrauchenia, Megatherium, Megalonyx, Mylodon, and
Glyptodon--this full of interest. His discovery of the remains of a true
Equus afforded a remarkable confirmation of the fact- -already made
out in North America--that species of horse had existed and become
extinct in the New World, before their introduction by the Spaniards in
the sixteenth century. Fully perceiving the importance of the
microscope in studying the nature and origin of such deposits as those
of the Pampas, Darwin submitted many of his specimens both to Dr.
Carpenter in this country, and to Professor Ehrenberg in Berlin. Many
very important notes on the microscopic organisms contained in the
formation