Towards the east they lie at a lower level; but in the Andes they reach a height of nearly 10,000 ft., and are strongly folded, showing that the elevation of the chain was not completed until after their deposition.
During the Tertiary period the great volcanoes of the Andes were formed, and there were smaller eruptions in the Sierras.
Farther south, in Patagonia, the prevailing wind is westerly, in which case the Andes again " blanket " an extensive region and deprive it of rain, turning it into an arid desolate steppe.
The Antarctic beech and Winter's bark (Drimys Winteri) are found at intervals along the Andes to the northern limits of this zone.
On the lower slopes of the Andes are found oak, beech, cedar, Winter's bark, pine (Araucaria imbricata), laurel and calden (Prosopis algarobilla).
