The crust of the earth, so far as it is permeable and above the sea-level, receives from rainfall its supply of fresh water.
The conception of a semi-permeable membrane, permeable to the solvent only, was used by van't Hoff as a means of applying the principles of thermodynamics to the theory of solution.
On the upheaval of such rocks above the sea-level, fresh water from rainfall began to flow over their exposed surfaces, and, so far as the strata were permeable, to lie in their interstices upon the salt water.
Known as confined aquifers, they are pools of fresh water trapped in permeable rock strata at depths of 300 to 6,000 feet.
This is reflected in unprecedented June runoff totals for some southern rivers draining permeable catchments.