Off the latter coasts there is a remarkable archipelago. Some of the islands are bold masses of arid rock, the resort of seafowl; others are arable and inhabited, while the actual coast fringes off into innumerable islets, some of which are immersed by the spring tides. In the channels scoured among these by the tremendous rush of the tide, navigation is ofttimes dangerous. Great mud-banks, specially near the mouths of the rivers, render parts of the coast-line dubious. Korea is decidedly a mountainous country, and has few plains deserving the name. In the north there are mountain groups with definite centres, the most remarkable being Paik-tu San, which attains an altitude of over 8,000 feet, and is regarded as sacred. Farther south these settle into a definite range, following the coast-line at a moderate distance, and throwing out so many ranges and spurs to the west as to break up northern and central Korea into a congeries of corrugated and precipitous hills, either denuded or covered with _chapparal_, and narrow, steep-sided valleys, each furnished with a stony stream. The great axial range, which includes the “Diamond Mountain,” a region containing exquisite mountain and sylvan scenery, falls away as it descends towards the southern coast, disintegrating in places into small and often infertile plains. The geological formation is fairly simple. Mesozoic rocks occur in Hwang-hai Do, but granite and metamorphic rocks largely predominate. Northeast of Seoul are great fields of lava, and lava and volcanic rocks are of common occurrence in the north. The climate is undoubtedly one of the finest and healthiest in the world. Foreigners are not afflicted by any climatic maladies, and European children can be safely brought up in every part of the peninsula. July, August, and sometimes the first half of September, are hot and rainy, but the heat is so tempered by sea breezes that exercise is always possible. For nine months of the year the skies are generally bright, and a Korean winter is absolutely superb, with its still atmosphere, its bright, blue, unclouded sky, its extreme dryness without asperity, and its crisp, frosty nights. From the middle of September till the end of June, there are neither extremes of heat nor cold to guard against. The summer mean temperature at Seoul is about 75° Fahrenheit, that of the winter about 33°; the average rainfall 36.03 inches in the year, and the average of the rainy season 21.86 inches.[2] July is the wettest month, and December the driest. The result of the abundant rainfall, distributed fairly through the necessitous months of the year, is that irrigation is necessary only for the rice crop.