The sector of Petit Pujeaux, or Poujeaux, is marked by limestone from the Late Eocene epoch (38 to 34 million years), clayey-marl limestone and compact or less compact Saint-Estèphe limestone. The Eocene epoch spans from 53 to 34 million years ago and is divided into three periods. The oldest period, Early Eocene, is a generally cold period during which only sand was deposited. The intermediary period, Middle Eocene, with a warm and humid climate, was very fertile in massive limestone beds. The Late Eocene period was more temperate, marked by more clayey limestone and the presence of marl.
In the Petit Poujeaux area, the erosion caused by the Tiquetorte stream, a major ground-water trench, and its tributaries, dissected the limestone bedrock to form a hand shape. This soil configuration, that is typical of the clayey-limestone base of a gravel terrace, allows natural drainage and ensures good drying of the soil. The sites of the Château Biston-Brillette terroirs are located at the bottom of the ledge and the slope of the clayey-limestone terrace of Moulis, from 17 to 9 metres. These terroir sites are conducive to wines of strength and colour. Today, they are the ideal terroir for Merlot, Cabernet Franc and Petit Verdot, in warm regions. With fine wines from gravel soils, these clayey-limestone wines have always been very successful in the past, and still are today.