Geological Observations on South America | Page 9

retraction of the views which had been put forward by
Murchison and Geikie in opposition to the conclusions of Darwin. The
officers of the Geological Survey have completely abandoned the view
that the foliation of the Highland rocks has been determined by their
original stratification, and admit that the structure is the result of the
profound movements to which the rocks have been subjected. The same
conclusions have recently been supported by observations made in
many different districts--among which we may especially refer to those
of Dr. H. Reusch in Norway, and those of Dr. J. Lehmann in Saxony.

At the present time the arguments so clearly stated by Darwin in the
work before us, have, after enduring opposition or neglect for a whole
generation, begun to "triumph all along the line," and we may look
forward confidently to the near future, when his claim to be regarded as
one of the greatest of geological discoverers shall be fully vindicated.
JOHN W. JUDD.
CHAPTER I.
ON THE ELEVATION OF THE EASTERN COAST OF SOUTH
AMERICA.
Upraised shells of La Plata. Bahia Blanca, Sand-dunes and
Pumice-pebbles. Step-formed plains of Patagonia, with upraised Shells.
Terrace-bounded Valley of Santa Cruz, formerly a Sea-strait. Upraised
shells of Tierra del Fuego. Length and breadth of the elevated area.
Equability of the movements, as shown by the similar heights of the
plains. Slowness of the elevatory process. Mode of formation of the
step-formed plains. Summary. Great Shingle Formation of Patagonia;
its extent, origin, and distribution. Formation of sea-cliffs.
In the following Volume, which treats of the geology of South America,
and almost exclusively of the parts southward of the Tropic of
Capricorn, I have arranged the chapters according to the age of the
deposits, occasionally departing from this order, for the sake of
geographical simplicity.
The elevation of the land within the recent period, and the
modifications of its surface through the action of the sea (to which
subjects I paid particular attention) will be first discussed; I will then
pass on to the tertiary deposits, and afterwards to the older rocks. Only
those districts and sections will be described in detail which appear to
me to deserve some particular attention; and I will, at the end of each
chapter, give a summary of the results. We will commence with the
proofs of the upheaval of the eastern coast of the continent, from the
Rio Plata southward; and, in the Second Chapter, follow up the same
subject along the shores of Chile and Peru.

On the northern bank of the great estuary of the Rio Plata, near
Maldonado, I found at the head of a lake, sometimes brackish but
generally containing fresh water, a bed of muddy clay, six feet in
thickness, with numerous shells of species still existing in the Plata,
namely, the Azara labiata, d'Orbigny, fragments of Mytilus eduliformis,
d'Orbigny, Paludestrina Isabellei, d'Orbigny, and the Solen Caribaeus,
Lam., which last was embedded vertically in the position in which it
had lived. These shells lie at the height of only two feet above the lake,
nor would they have been worth mentioning, except in connection with
analogous facts.
At Monte Video, I noticed near the town, and along the base of the
mount, beds of a living Mytilus, raised some feet above the surface of
the Plata: in a similar bed, at a height from thirteen to sixteen feet, M.
Isabelle collected eight species, which, according to M. d'Orbigny, now
live at the mouth of the estuary. ("Voyage dans l'Amerique Merid.: Part.
Geolog." page 21.) At Colonia del Sacramiento, further westward, I
observed at the height of about fifteen feet above the river, there of
quite fresh water, a small bed of the same Mytilus, which lives in
brackish water at Monte Video. Near the mouth of Uruguay, and for at
least thirty-five miles northward, there are at intervals large sandy tracts,
extending several miles from the banks of the river, but not raised
much above its level, abounding with small bivalves, which occur in
such numbers that at the Agraciado they are sifted and burnt for lime.
Those which I examined near the A. S. Juan were much worn: they
consisted of Mactra Isabellei, d'Orbigny, mingled with few of Venus
sinuosa, Lam., both inhabiting, as I am informed by M. d'Orbigny,
brackish water at the mouth of the Plata, nearly or quite as salt as the
open sea. The loose sand, in which these shells are packed, is heaped
into low, straight, long lines of dunes, like those left by the sea at the
head of many bays. M. d'Orbigny has described an analogous
phenomenon on a greater scale, near San Pedro on the river Parana,
where he found widely extended beds and hillocks of sand, with vast
numbers of the Azara labiata, at the height