THE grikes, or channels, frequently formed by the corrosive action of carbonic and organic acids upon the surfaces of exposed limestone beds are known to most geologists, but a case I recently met ...

IN the Lower Old Red Sandstone of the west of Caithness I have noticed an appearance which recalls the grikes due to erosion of which Mr. Carus-Wilson writes in NATURE of May 1. It is seen in the ...

Why it's incredible: The rock formation is split cleanly down the middle as if cut by a laser. The Al Naslaa Rock Formation is a landmark in the Saudi Arabian desert formed of two big blocks of ...