Why does the proportion of unweathered rock increase with depth?

Question

Why does the proportion of unweathered rock increase with depth?

Answer 1

Weathering occurs on the surface, whether you are talking about water effects or wind and sand or chemical. Therefore there would be less in rocks further under the surface.

Answer 2

Because the deeper the rock, the less exposed it is to the weather. If the rain and ice can't get at it, it won't be as "weathered" as the layers closer to the surface.