The Geology of the Central Andes in Part of the Province of Junin, Peru

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Abstract
Summary An area of 2500 square miles in the Department of Junin was geologically and topographically surveyed. Sediments and lavas up to a thickness of 26,000 feet were laid down upon folded Devonian or older beds in a trough which was flooded by stages. Volcanic and intrusive rocks are interspersed at many horizons. Spilites are interbedded with the lowest group, which is cut by peridotite. Rhyolitic flows and breccias mark the Carboniferous. Teschenite sills pierce many horizons of the Mesozoic and small plugs of granite and quartz-porphyry were intruded during the early Mesozoic stages. Cretaceous and later sediments in the western Cordillera were altered by intrusive bodies, but the granites of the eastern Cordillera are probably older than Cretaceous. Strong folding preceded the deposition of the Carboniferous and'a second major movement took place after the Bed Bed Series had been laid down. Warping affected beds of Carboniferous, Trias, Lias and Cenomanian ages. The Trias and Lower Lias are overlapped by the Middle Lias. A gap probably exists between this and the Lower Cretaceous, and the rapid thickening of the Red Bed Series suggests the existence of a gap also between it and the Cenomanian, with some disturbance, though of lesser magnitude than the main folding which affects the Red Bed Series and its suite of lavas. Topographical evidence is interpreted to mean that an uplift of some 10,000 feet took place during Pleistocene time. I . Introduction This paper has been written mainly as a commentary and explanation of the