The grandfather of the wine regions of Bordeaux is Graves, on the left bank of the Garonne as it heads north west to join the Dordogne. The land is characterised by intensely gravelly soil - glacial deposits - and though this engenders fine drainage properties, all those stones must be a nightmare for farmers and their machinery. However, if it's grapes you're growing this otherwise troublesome terrain is a positive blessing for, it is said, not only is the land free draining, but the pale pebbles reflect light and heat up under the fruit, aiding ripening.
I'll take this on trust. Sante!