Since that time only slight tremors have been felt. The internal heat in the north-eastern spur of the Andes, which traverses Venezuela, manifests itself at many points in the form of hot springs. One, containing much sulphur, is found at Las Trincheras, between Valencia and Puerto Cabello. The temperature of this spring varies, but in 1852 it was found by Karsten to be only a few degrees below the boiling point of water; in general, however, it does not exceed 195° F. or 17° below boiling point. Wall found one south of Carúpano actually boiling. All along the flanks of the coastal Cordillera there are mineral springs, generally at fairly high temperatures, and many more are known throughout the Andes. Nearly all these springs have been used in the treatment of various diseases, though none has achieved especial popularity. While hot springs may be interesting to the visitor, they are hardly valuable assets to a country such as Venezuela, but this part of the world has always, and with much justice, held the reputation of being rich in minerals. There is coal of fairly good quality in more than one of the Cretaceous and Tertiary groups of strata, near Barcelona, Tocuyo, Coro, and Maracaibo, as well as in the Andes, but the often-associated iron is only found in large quantities in the Guayana gneiss south of the Orinoco Delta. Gold, that great lure for the early European ventures to the west, may be said to occur in almost every State of Venezuela, but it has only been worked with profit in Guayana, even though samples of a quartz-reef near Carúpano are said to have assayed 7 oz. to the ton. When Sir Robert Dudley visited the coast of the Gulf of Paria in 1595, he heard of a goldmine near Orocoa (Uracoa), on the eastern side of the Llanos, which may mean that the gravels are occasionally auriferous, but unfortunately he failed to reach the place. Placer workings are the chief source of the precious metal in the Guasipati goldfields in Guayana, but the reefs from which it is derived have been discovered and worked at odd times. In British Guiana, where the conditions are similar, Mr. Harrison says that the gold is generally found along the later intrusive dykes, the smallest dykes being the richest, while most gold is found where a basalt intrusion crosses one of the older ones. The ores of copper are fairly common in the northern Cordillera, and the mines of Aroa in Yaracuy have been worked for many years. Here the pyrites veins occur in the Capacho Limestone, not far from where it has been invaded by a mass of granite. In the Andes it seems to occur in the more ancient rocks, as near Seboruco in Táchira, and Bailadores in Mérida. A mine near Pao seems to be in Cretaceous rocks.