ting into the
sea. South of Antofagasta the old rocks form a nearly continuous band
along the coast, extending as far as Cape Horn and Staten Island, and
occupying the greater part of the islands of southern Chile.
Lithologically they are crystalline schists, together with granite,
diorite, gabbro and other igneous rocks. They are known to be
pre-Jurassic, but whether they are Palaeozoic or Archaean is
uncertain. They are strongly folded and are overlaid unconformably by
Cretaceous and Tertiary deposits. In the north both the Cretaceous and
Tertiary beds of this zone are limited in extent, but towards the
south Mesozoic beds, which are at least in part Cretaceous, form a
band of considerable width. The Tertiary beds include both marine and
terrestrial deposits, and appear to be chiefly of Miocene and Pliocene
age. The whole of the north part of Tierra del Fuego is occupied by
plateaus of horizontal Tertiary strata.

The Chilean Andes correspond with the Western Cordillera of Bolivia
and Peru, and consist almost entirely of Jurassic and Cretaceous beds,
together with the products of the Tertiary eruptions. The Mesozoic
beds are thrown into a series of parallel folds which run in the
direction of the chain and which are generally free from any
complications such as overthrusting or overfolding. The Cretaceous
beds form a synclinal upon the eastern side of the chain (and, in
general, beyond the Chilean boundary), while the Jurassic beds are
thrown into a number of folds which form the axis and the western
flank. Through the Mesozoic beds are intruded granitic and other
igneous rocks of Tertiary age, and upon the folded Mesozoic foundation
rise the volcanic cones of Tertiary and later date. The Trias is known
only at La Ternera near Copiapo, where coal-seams with Rhaetic plants
have been found; but the rest of the Mesozoic series, from the Lias to
the Upper Cretaceous, appears to be represented without a break of
more than local importance. The deposits are marine, consisting mainly
of sandstone and limestone, together with tuffs and conglomerates of
porphyry and porphyrite. These porphyritic rocks form a characteristic
feature of the southern Andes, and were at one time supposed to be
metamorphic; but they are certainly volcanic, and as they contain
marine fossils they must have been laid down beneath the sea. They are
not confined to any one horizon,