The space between the Cordillera and the coast of Chile is on a rude
average from eighty to above one hundred miles in width; it is formed,
either of an almost continuous mass of mountains, or more commonly of
several nearly parallel ranges, separated by plains; in the more southern
parts of this province the mountains are quite subordinate to the plains;
in the northern part the mountains predominate.

The basin-like plains at the foot of the Cordillera are in several respects
remarkable; that on which the capital of Chile stands is fifteen miles in
width, in an east and west line, and of much greater length in a north and
south line; it stands 1,750 feet above the sea; its surface appears smooth,
but really falls and rises in wide gentle undulations, the hollows
corresponding with the main valleys of the Cordillera: the striking manner
in which it abruptly comes up to the foot of this great range has been
remarked by every author since the time of Molina. (This plain is partially
separated into two basins by a range of hills; the southern half, according
to Meyen ("Reise um Erde" Th. 1 s. 274), falls in height, by an abrupt
step, of between fifteen and twenty feet.) Near the Cordillera it is
composed of a stratified mass of pebbles of all sizes, occasionally
including rounded boulders: near its western boundary, it consists of
reddish sandy clay, containing some pebbles and numerous fragments of
pumice, and sometimes passes into pure sand or into volcanic ashes. At
Podaguel, on this western side of the plain, beds of sand are capped by a
calcareous tuff, the uppermost layers being generally hard and
substalagmitic, and the lower ones white and friable, both together
precisely resembling the beds at Coquimbo, which contain recent marine
shells. Abrupt, but rounded, hummocks of rock rise out of this plain: those
of Sta. Lucia and S. Cristoval are formed of greenstone-porphyry almost
entirely denuded of its original covering of porphyritic claystone breccia;
on their summits, many fragments of rock (some of them kinds not found in