The beds of marl found in the Coastal Plain have already been mentioned. This region also contains very valuable beds of white sand and fine clay. This sand is used in the making of glass, and has caused the establishment of many glass factories in the southwestern part of the state. Molding sand is also found in great quantity. The most extensive beds of clay are found in Mercer and Middlesex counties. In the former they are used in the making of pottery and in the latter in the making of brick, terra cotta, tile, and other clay products. The enormous industries of Trenton and of Perth Amboy and its vicinity are due to the presence of these clays. For the finer pottery, clays brought from other states or countries are used. Much clay is shipped from this state to other states. [Illustration: Pottery works, Trenton] =Manufacturing.=--New Jersey is an important manufacturing state. In this state the manufacturing industries have been developed in a remarkable degree by a combination of conditions and causes. Very early in the history of New Jersey the people of the state were forced by their own needs and the demands of their neighbors to establish manufacturing, and thus this industry has the advantage of many years of growth. The state is rich in certain important natural resources, which have been mentioned. It has profited greatly by its nearness to the coal and iron fields of Pennsylvania and to the two great cities of New York and Philadelphia, with their enormous demands for manufactured products. The number of intelligent and skillful workers in the state is unusually large. The facilities for rapid transportation, both of raw materials from all sources and of finished products to all markets, are unusually abundant. The navigable waters which fringe the state, and the transcontinental railroad systems with their branches, which cross it, facilitate shipments to every part of the world. Among the most important manufactures of New Jersey are refined copper, silk and silk goods, foundry and machine shop products, petroleum products, packed meats, woolen and felt goods, wire, leather and leather goods, electrical machinery, tobacco manufactures, chemicals, and ships. (See Table II for other manufactures.) [Illustration: Warping silk, silk mills, Paterson] [Illustration: Weaving silk, Paterson]