Magellan, that the entire width of the plain, although there very narrow,
has been elevated. It is probable that in this southernmost part of the
continent, the movement has extended under the sea far eastward; for at the
Falkland Islands, though I could not find any shells, the bones of whales
have been noticed by several competent observers, lying on the land at a
considerable distance from the sea, and at the height of some hundred feet
above it. ("Voyages of the 'Adventure' and 'Beagle'" volume 2 page 227. And
Bougainville's "Voyage" tome 1 page 112.) Moreover, we know that in Tierra
del Fuego the boulder formation has been uplifted within the recent period,
and a similar formation occurs on the north-western shores (Byron Sound) of
these islands. (I owe this fact to the kindness of Captain Sulivan, R.N., a
highly competent observer. I mention it more especially, as in my Paper
(page 427) on the Boulder Formation, I have, after having examined the
northern and middle parts of the eastern island, said that the formation
was here wholly absent.) The distance from this point to the Cordillera of
Tierra del Fuego, is 360 miles, which we may take as the probable width of
the recently upraised area. In the latitude of the R. Santa Cruz, we know
from the shells found at the mouth and head, and in the middle of the
valley, that the entire width (about 160 miles) of the surface eastward of
the Cordillera has been upraised. From the slope of the plains, as shown by
the course of the rivers, for several degrees northward of the Santa Cruz,
it is probable that the elevation attested by the shells on the coast has
likewise extended to the Cordillera. When, however, we look as far
northward as the provinces of La Plata, this conclusion would be very
hazardous; not only is the distance from Maldonado (where I found upraised
shells) to the Cordillera great, namely, 760 miles, but at the head of the
estuary of the Plata, a N.N.E. and S.S.W. range of tertiary volcanic rocks
has been observed (This volcanic formation will be described in Chapter IV.
It is not improbable that the height of the upraised shells at the head of
the estuary of the Plata, being greater than at Bahia Blanca or at San