During the Jurassic there appeared very thick capes of volcanic lava: porphyrits in the Central Andes, porphyry and quarz in Patagonia.
In the Patagonian Pampa you find today continental sediments (schists) of cretaceous, alternating with marines (sandy and arenaceous). In the Central Andes during the inferior cretaceous continue effusions of porphyrits with some deposits of fossiliferous limestone (sometimes transformed later in gypsum) and arenaceous. During the medium cretaceous (senonense) the marine conglomerations of Quiriquina are placed on some points of the coast.
The inferior tertiary (eocenen) is continental but in the medium tertiary (oligocene) there was a great marine invasion. During the end of the Miocene and the inferior Pliocene came the great effusions of andesites, trachytes and basalts, as well in the frontier cordon as in all the Patagonian plateaux in the East of the Cordillera.

You have to distinguish between the folds and elevations of the Cordillera. A1 the Andean folds occurred during the medium cretaceos, but only a part of its elevation follows during the tertiary forming a plain which was raised later to 3.000 m of the Andes.

The submersion of the Central valley succeeded during the ' superior Pliocene' before the great glaciations and still continues. As a matter of fact the raising of the Andes and the submersion of the Central Valley was created slowly (even on geological escale) and possibly during many cycles.

Just like greater part of the Central Andes, this point is constituted by acid lavas: porphyrits of apparent grains, but without Phenocristals. It is atributed to the cretaceous, because more to the East (Polleras and Alto Yeso) there are interlarded limestone capes rich in fossils of inferior cretaceous.

The force of these porphyrit capes is of more than 3.000 m and its stratification is horizontal except in the South East part, from where they fall to the East and are vertical in the Tronco hill.

The knot of the Nevado Juncal (frontier Argentine-Chile) corresponds essentially to a high rectangular plateau of 21 x 8 kilometers with extension North East - South West with a height between 3.600 and 4.600 meters and with two parapetes on its extremities: the Nevado Juncal in the North West and the group of Plomo hill in the South West. This high plateau is nearly completely covered by five glaciers. The glacier Escondido, the three glaciers Olivares and the glacier Juncal (South). The first flows to the north and the other four to the South.
Generally the climate of the Andes is determined by various factors: the marine currents of Humboldt and Patagonians, the winds and orography.

The currents of Hunboldt (cold) and Patagonian (tempered) irrigate the North and South coasts of Chile respectively. That is to say that the climate of the Central Andes is determined by the winds and their orography. As the predominant wind is dry from South West there are no precipitations and no clouds in summer. The precipitations are always in the form of snow in the great heights; rain is unknown.

On sunny days, between 10 am and 2 pm the air temperature near the ground goes up strongly. Normally, vetical convection would be produced above any regular plain. In the Cordillera, on the other hand, the rising of air takes place along the valleys and hill sides, which act like ch~mmeys. The pressure on the tops is considerably low. This breeze (from the valley) provokes in the afternoon the formation of cumulus. From January to April the air in the Andes is so dry that the c~nulus can not arrive to a formation in spite of the breeze of valley. In the night it is the contrary, and a cold breeze comes from the Cordillera to the Central Valley.'
Around 35° South latitude the high s~u~mits begin to take shape and so does the area where except for scarce and brief storms~ the summer is absolutely dry.

This part of the Andean Cordillera is characterized by three phenomena:

1 ° The omnipresence of penitent camps above 4.000 o 5.000 meters, due to the long dry season.
2° Low development of snow. The glaciers subsist exclusively by recongelation and not by snow compression.
3° The abundance of subterranian glaciers covered by alluvium material.