We have measured cosmic ray produced 10Be (t1/2=1.5 My) and 26Al (t1/2=0.72 My) as functions of depth in a core of quartz sandstone bedrock collected in South Victoria Land, Antarctica. These data were used to place limits on the exposure age and erosion rate of the exposed surface, and to calculate the effective attenuation lengths of cosmic rays producing these nuclides. These latter results indicate that the production attenuation length for 26Al (156 -12+13 g cm-2) is comparable to that for 10Be (145 -6+8 g cm-2). This suggests that the production ratio 26Al:10Be does not vary substantially with depth in a rock, and that its value at the surface of exposed rock is not strongly affected by erosional losses, allowing wider use of the ratio in determining exposure ages. ¿ American Geophysical Union 1992