Parchappe, however, has described groups of sand dunes scattered over the
wide extent of the Pampas southward of Buenos Ayres (D'Orbigny "Voyage
Geolog." page 44.), which M. d'Orbigny attributes with much probability to
the action of the sea, before the plains were raised above its level.
(Before proceeding to the districts southward of La Plata, it may be worth
while just to state, that there is some evidence that the coast of Brazil
has participated in a small amount of elevation. Mr. Burchell informs me,
that he collected at Santos (latitude 24 degrees S.) oyster-shells,
apparently recent, some miles from the shore, and quite above the tidal
action. Westward of Rio de Janeiro, Captain Elliot is asserted (see Harlan
"Med. and Phys. Res." page 35 and Dr. Meigs in "Transactions of the
American Philosophical Society"), to have found human bones, encrusted with
sea-shells, between fifteen and twenty feet above the level of the sea.
Between Rio de Janeiro and Cape Frio I crossed sandy tracts abounding with
sea-shells, at a distance of a league from the coast; but whether these
tracts have been formed by upheaval, or through the mere accumulation of
drift sand, I am not prepared to assert. At Bahia (latitude 13 degrees S.),
in some parts near the coast, there are traces of sea-action at the height
of about twenty feet above its present level; there are also, in many
parts, remnants of beds of sandstone and conglomerate with numerous recent
shells, raised a little above the sea-level. I may add, that at the head of
Bahia Bay there is a formation, about forty feet in thickness, containing
tertiary shells apparently of fresh-water origin, now washed by the sea and
encrusted with Balini; this appears to indicate a small amount of
subsidence subsequent to its deposition. At Pernambuco (latitude 8 degrees
S.), in the alluvial or tertiary cliffs, surrounding the low land on which
the city stands, I looked in vain for organic remains, or other evidence of
changes in level.)

SOUTHWARD OF THE PLATA.