but occur irregularly throughout the
Jurassic and occasionally also amongst the Cretaceous strata. They
form, in fact, a special facies which may frequently be traced
laterally into the more normal marine deposit of the same age. The
fauna of the Mesozoic beds is very rich, and includes forms which are
found in northern Europe, others which occur in central Europe, and
others again which are characteristic of the Mediterranean region. It
lends no support to Neumayr's theory of climatic zones. A large part
of the chain is covered by the products of the great volcanoes which
still form the highest summits of the Chilean and Argentine Andes. The
rocks are liparites, dacites, hornblende and pyroxene andesites. The
recent lavas of the still active volcanoes of the south are
olivine-bearing hypersthene-andesite and basalt.[1]

_Climate_.--The climate of Chile varies widely, from the tropical
heat and extreme arid conditions of the northern coast to the low
temperatures and extreme humidity of western Tierra del Fuego and the
southern coast. The high altitudes of the Andean region also introduce
vertical zones of temperature, modified to some extent by the rainless
plateaus of the north, and by the excessive rainfall of the south. In
general terms it may be said that the extremes of temperature are not
so great as in corresponding latitudes of the northern hemisphere,
because of the greater expanse of water in comparison with the land
areas, the summers being cooler and the winters warmer. The cold
antarctic, or Humboldt, current sweeps northward along the coast and
greatly modifies the heat of the arid, tropical plateaus. The climate
of northern and central Chile is profoundly affected by the high
mountain barrier on the eastern frontier and by the broad treeless
pampas of Argentina, which raise the easterly moisture-laden winds
from the Atlantic to so high an elevation that they sweep across Chile
without leaving a drop of rain. At very rare intervals light rains
fall in the desert regions north of Coquimbo, but these are brought by
the prevailing coast winds. With this exception these regions are the
most arid on the face of the globe, highly heated by a tropical sun
during the day and chilled at night by the proximity of snow-covered
heights and a cold ocean current. Going south the temperature slowly
falls and the rainfall gradually increases, the year b