Puerto Rico has no mines or minerals of any consequence, except a little
iron. Foundries for magnetic iron have been established at Ponce, San
Juan and Mayaguez.
Gold, silver, copper and coal are known to exist in small quantities
beneath the surface, but not in sufficient amount to be mined.
The island is well supplied with limestone, which makes an excellent
building material. Marble, also, is easily obtained. Along the coast are
occasional marshes where salt is prepared for market.