Nature has been active in these regions. There is much limestone and slate formation, some basaltic upheavals, lava boulders, and chain upon chain of granite peaks. To the west of Tong-ko-kai there is the crater of an extinct volcano, but the lava _strata_ in the vicinity of the concession are almost completely eroded. The basin of the concession is well watered, cultivated, and populous in places. It is surrounded by ranges three, four and five thousand feet in height. Korea is very mountainous in the north and hilly in the south. The watershed between the Sea of Japan and the Yellow Sea extends north and south, nearly parallel to the east coast. In a sense this line of mountain ranges is the backbone of the peninsula; the eastern side of the main watershed is narrow and abrupt, while the western is more extended and contains low plains, favourable to agriculture. The general altitude of the peaks varies between five and six thousand feet. A few isolated points in the extreme north are believed to be higher. The principal mining districts are situated along the courses of the main and the minor watersheds. The famous mining districts of Kang-kyöi, Kap-san, and Teh-chang-chin, at present in the occupation of native workmen, occur upon the plateau formed by the junction of the range, which constitutes the northern frontier of the province of Pyöng-an, with the main watershed of the country. The British mines at Eun-san are situated in country pierced by the north-western antilles of the main watershed. The position of the German mines bears a similar relation to the great natural division of the country, upon its eastern side. Many useful minerals are distributed over Korea—gold, silver, lead, copper, iron, coal—but that which yields the richest harvest is gold. The value of the gold exported from Korea during 1901 increased from £363,305 in 1900 to £509,738. A further increase marks 1902, the value of the gold exported being £516,961. These figures give only the value declared at the Customs. Large amounts are annually smuggled out of the country. The presence of gold has been known from the earliest times. Knochenhauer, a German geologist, has declared it to exist in every river in the kingdom. Hitherto, alluvial gold has been the principal yield to native workers. The miners followed the object of their search up the mountain side until they struck veins and lodes, whence much of the alluvial gold was derived. The chief auriferous districts are in the northern half of the country; in which sphere lie the American mine at Un-san, the British mine at Eun-san, and the German mine at Tong-ko-kai.