New field work is reported in the Andes. A belt of complex structure is discussed and described. Narrow folds and thrust faults involved Paleozoic to Tertiary rocks. Cretaceous limestone is exposed in a sheet that was thrust from the southwest. Younger tectonics were related to the formation of the Yauli dome during the Tertiary. Reverse faults at the surface change to northeast directed thrusts at depth. Evidence for overthrusting is apparent in the repetition of the Pariatambo and Jumasha formations. Extension of structural features earlier mapped by Harrison shows complexities equal to those of the Jura in Europe. Diastrophism cannot be definitely dated but probably was restricted to middle and late Tertiary.

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