The most northerly outcrop of the Burgundy catchment is famous for its combination of Chardonnay and soil, in this case a mix of rocks dating back to the Jurassic age (180 million years old) that deliver steely and intense wines. Kimmeridgean soils, a mix of limestone and clay riddled with fossilised oyster shells give the A.C. wines, the Premiers Cru and Grands Cru such distinctive character. Portlandian soils deliver more forward and open wines and are the basis of much of the surrounding Petit Chablis area. Frost is a major issue and exposition is paramount in Chablis, with the Grand Cru sites lined up shoulder to shoulder, like folded soldiers saluting the southern sun. There are seven Grand Cru vineyards; from east to west they are Bougros, Les Preuses, Vaudesir, Grenouilles, Valmur, Les Clos and Blanchots. The premier cru sites are again decided more by exposure than soil, in particular on the left bank side of the region where the Côte de Lechet delivers a distinctive, racy appeal. The best known premier cru sites are: Fourchaume, Monteé de Tonnerre, Mont de Milieu, Vaucoupin, Vosgros, Montmains, Vaillons (including Les Lys) and Côte de Lechet.