The segment of the Argentine Andes between lat 41°10' S. and lat 43°10' S. was formerly occupied by a thick mountain ice sheet, which in places spread as far east as long 71° W. The eastern limit of glaciation determined by us is broadly similar to that fixed by Caldenius in 1932, although it differs in detail.
We have separated the glacial drift in the area into three units, defined on a semiquantitative basis of degree of weathering of granitic clasts. This three-fold sequence contrasts with a sequenceof four units proposed by Caldenius. The intensity of weathering of our two older units is considerable. It seems to us too great to be compatible with the dates implied by Caldenius' correlation with drift, in Sweden, dated according to the time scale of De Geer. However, the weathering displayed by the drift in the Argentine area could reasonably have developed within a time interval no longer than that generally ascribed to the Wisconsin Age (in the wide sense) in North America, although the oldest drift could conceivably be pre-Wisconsin.