This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
South African Geology Schwarz Fig . en Figure from South African Geology Schwarz Page Fig Snuff box Shale upper Dwyka shales weathering from within The cementing material of the rock becomes concentrated along the joints leaving the interior of the blocks white and pulverulent File South African Geology Schwarz djvu