The Comte Tolosan region used to go by a different name. Because of its prevalent thermal springs, rivers, and lakes; Julius Caesar dubbed the region Aquitaine, the land of waters. In fact, Caesar didn't know the half of it.
The wonderful vineyard soil of the region today was actually made possible by geological processes started hundreds of millions of years ago when Europe was a volcanic mess! The two mountain ranges on the east and south of the region created the second largest sedimentary basin in France with its middle tilting and forming a funnel toward the Atlantic. The well-draining rocky soils are perfect for vines and the ocean-fed maritime climate moderates any temperature extremes.
So the basin was created during the Triassic and Permian Ages, 200-300 million years ago. Since then alluvial soils have filled in the rock bottom to about 11,000 meters and the deepest trench follows the course of the Garonne River northeastward toward Bordeaux. Not surprisingly most of the Comte Tolosan vineyards are located centrally along the Garonne River over the abyss.
Land of waters indeed, Julius.