Geologically we meet with a regular succession of formations, from the granite on the mountain summits to the alluvial deposits along the banks of the Danube. The rocks encountered on these southern slopes of the Carpathians are of the same kind as those found in Galicia on their northern slopes, and they yield the same mineral products, such as rock-salt, gypsum, lithographic stones, and petroleum. Tertiary strata predominate in the plains, but to the east of Ploiesti and Bucharest only quaternary deposits of clay and pebbles are met with, in which are found the bones of mammoths, elephants, and mastodons. The muddy rivers which traverse these plains have excavated themselves sinuous beds, and resemble large ditches. The plain of Rumania, like that of Lombardy, is an ancient gulf of the sea filled up by the débris washed down from the mountain sides. But though the sea has retired, the Danube remains, pouring out vast volumes of water, and offering great advantages to navigation. At the famous defile of the Iron Gate, where this river enters the plain, its bed has a depth of 155 feet, its surface lies 66 feet above the level of the Black Sea, and its volume exceeds that of the combined rivers of Western Europe, from the Rhone to the Rhine. The Romans, in spite of this, had thrown a bridge across the river, immediately below the Iron Gate, which was justly looked upon as one of the wonders of the world. This work of architecture, which Apollodorus of Damas had erected in honour of Trajan, was pulled down by order of the Emperor Hadrian, who was anxious to save the expenses of the garrison required for its protection. There only remain now the two abutments, and when the waters are low the foundations of sixteen out of the twenty piers which supported the bridge may still be seen. A Roman tower, which has given name to the little town of Turnu Severin, marks the spot where the Romans first placed their foot upon the soil of Dacia. The passage from Servia to Rumania is as important as it was of yore, but modern industry has not yet replaced Trajan’s bridge.