I thoroughly recommend both of these stories. Both are concerned with the processes of time, and their effect on the natural world. I particularly enjoyed 'The Crystal World', with it's vivid descriptions of a tropical jungle slowly crystallising...
"...what surprised me most..was the extent to which I was prepared for the transformation of the forest - the crystalline trees hanging like icons in those luminous caverns, the jewelled casements of the leaves overhead, fused into a lattice of prisms, through which the sun shone in a thousand rainbows, the birds and crocodiles frozen into grotesque postures like heraldic beasts carved from jade and quartz..." Again, I am reminded of Robert Smithson, and his obsession with crystallography.
The Drowned World cover shows Le Palais aux Rochers de Fenetres (1942), by Yves Tanguy
The Crystal World shows Max Ernst's The Eye of Silence (1943)