The outer coastal plain consists of unconsolidated Tertiary deposits of sands, silt, and gravels. The soils are sandy with less clay than the inner coastal plain, and are more acidic and dry. The lack of fertility makes much of the region unsuitable for agriculture and large areas remain undeveloped. The sandy Pine Barrens, an area that is agriculturally poor but species rich, occupy the center of the province. Blueberries and cranberries have been cultivated in lowland bogs that have accumulated depths of organic matter.