Morphological and weathering characteristics of a group of tors, possessing both anular and rounded joint-blocks, at Sandy Glacier (Wright Valley) in the McMurdo “oasis” of southern Victoria Land are described. Clay minerals (kaolinite family) at and beneath the surface of the rounded corestones indicate chemical weathering of the dolerite. The juxtaposition of rounded and angular tors on the summit of the arête is explained in terms of local variations in microclimate, especially as it affects snow cover. Both types of tor are the product of the prevailing polar desert conditions. It is concluded that such conditions have probably prevailed here throughout the Pleistocene with only brief episodes of slightly more maritime climate.