That part of Tonquin known as the Yen-Thé region is bordered on the south and west by the Song-Cau river, on the east by the Song-Thuong, and on the north by a chain of rocky heights running from Thaï-Nguyen to Vanh-Linh, which is situated a little to the north of the new railway from Phulang-Thuong to Lang-son. The southern part of it, which is generally designated as the Lower Yen-Thé, is an immense plain rising gradually to the north, and studded here and there with small isolated groups of hills, none of which exceed 500 feet in height. It is traversed by numerous streams all running into the Song-Thuong and Song-Cau rivers, and to these the district owes its wonderful fertility. The soil of this region is composed of a dull-red clay, containing innumerable small round pebbles. It does not produce such fine rice as the black alluvial mud plains of the Delta, but it is better adapted than these for the growing of yams, tobacco, the mulberry tree and castor-oil plant. About 20 miles north of Phulang-Thuong this plain terminates, and it is succeeded by a mass of hills which here and there enclose small marshy plains. The country is overrun by dense forests, into which a few paths, made by charcoal burners, offer the only means of penetration. It would need a master-pen to produce an adequate description of the savage wildness of this region, which teems with game. Tigers, panthers, bears, many kinds of deer, wild pigs and boars abound; peacocks, silver-pheasants, partridges and snipe are very numerous. For centuries past the Tonquinese have associated the Upper Yen-Thé with the mysterious and the supernatural. Native folk-lore declares that a former Emperor, thanks to a powerful magic he possessed, succeeded in driving from the lowlands a race of cruel and wicked genii. To escape complete destruction these fled into the forests, where, so runs the legend, they still live and guard the rich mineral treasures which are said to exist there. The native of the Delta possesses a real dread of this part of the country, for, not only is the Tonquinese the most superstitious of humans, but the lowlander who comes into these regions is speedily attacked by a virulent form of paludo-hæmaturic fever, which in most cases terminates fatally. It was owing principally to these reasons that the native troops, with the exception of the few companies recruited from the Muong tribes, were of small service during the operations which took place there. In this maze of hills, covered by virgin forests, rank swamp and deep jungle, De-Nam established his headquarters in 1887. He was no commonplace individual, this Asiatic; indeed, when one considers his subsequent career, it is impossible to repress a sentiment of admiration for this man, who, during the four years he led the rebellion, proved himself to be a capable administrator, a talented military engineer, and a clever and a daring general.