at the height of 100 feet beds of the Azara, the space in a north and south
line, which has been uplifted within the recent period, must have been much
above the 1,180 miles. By the term "recent," I refer only to that period
within which the now living mollusca were called into existence; for it
will be seen in the Fourth Chapter, that both at Bahia Blanca and P. S.
Julian, the mammiferous quadrupeds which co-existed with these shells
belong to extinct species. I have said that the upraised shells were found
only at intervals on this line of coast, but this in all probability may be
attributed to my not having landed at the intermediate points; for wherever
I did land, with the exception of the river Negro, shells were found:
moreover, the shells are strewed on plains or terraces, which, as we shall
immediately see, extend for great distances with a uniform height. I
ascended the higher plains only in a few places, owing to the distance at
which their escarpments generally range from the coast, so that I am far
from knowing that 410 feet is the maximum of elevation of these upraised
remains. The shells are those now most abundant in a living state in the
adjoining sea. (Captain King "Voyages of 'Adventure' and 'Beagle'" volume 1
pages 6 and 133.) All of them have an ancient appearance; but some,
especially the mussels, although lying fully exposed to the weather, retain
to a considerable extent their colours: this circumstance appears at first
surprising, but it is now known that the colouring principle of the Mytilus
is so enduring, that it is preserved when the shell itself is completely
disintegrated. (See Mr. Lyell "Proofs of a Gradual Rising in Sweden" in the
"Philosophical Transactions" 1835 page 1. See also Mr. Smith of Jordan Hill
in the "Edinburgh New Philosophical Journal" volume 25 page 393.) Most of
the shells are broken; I nowhere found two valves united; the fragments are
not rounded, at least in none of the specimens which I brought home.

With respect to the breadth of the upraised area in an east and west line,
we know from the shells found at the Inner Narrows of the Strait of