Surah 56. Al-Waqia, Ayah 70

The wonder of the two streams of water, one sweet and the other salt, constantly mingling, and yet always separate, is referred to more than once. The never-ending circuit is established by streams and rivers mingling with the ocean, the ocean sending forth mists and steam through a process of evaporation which forms clouds, and the clouds by condensation pouring forth rain to feed the streams and rivers again: see notes 3111-2 to xxv. 53, and n. 5185 to lv. 19, and the further references given there.