For building purposes there is a large variety of limestone and lime. The coral rock is easy to quarry and soft enough to shape with the axe, but exposure to the air makes it hard as granite, as is proven by the old buildings and city walls of Santo Domingo City, which have stood for centuries. In the central range, on the Samana peninsula and near Puerto Plata, granite, syenite and other building stones are found, but owing to the absence of transportation facilities they are not utilized. In the Bani region a sandstone occurs from which grindstones are made. Clay of a fine grade, proper for the manufacture of bricks and tiles, is abundant. Clays of various colors, found in the interior of the island, are suitable for the manufacture of paints. Gypsum is found, especially in Azua province, and the presence of kaolin and feldspar in the province of Santo Domingo, south of the central range, offers a possibility of porcelain manufacture. Petroleum has been found in large quantities in the vicinity of Azua. The presence of the oil is suspected in other parts of the island and it is claimed that a petroleum belt which is believed to extend from Pennsylvania to Venezuela embraces a considerable portion of the Dominican Republic. Near Puerto Plata, during rains, one of the streams flowing down from the mountains in the Mameyes section, is covered with greasy spots thought to be petroleum that has oozed from the subsoil. Traces of petroleum have also been discovered near Neiba, and in the provinces of Pacificador and Seibo.