Armorican Massif
The Thouet rises in the Gâtine Vendéenne, the most southern outcrop of the Armorican Massif, at altitude. The Armorican Massif is made up of volcanic and metamorphic rocks dating back to the Paleozoic era. This impermeable land does not result in any important aquifers but is an area of significant rainfall runoff. From the source to Parthenay the river flows in a generally east-west direction.