GEOGRAPHY AND CLIMATE
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greater importance and there is currently an active mine at Ma On Shan, which exports concentrated ore to Japan.
Due to the hilly topography, agricultural land is extremely re- stricted. The most important area is the flat alluvium around Yuen Long in the Deep Bay area. Outside the alluvial areas, soil cover is usually thin, sometimes no more than two or three inches. In general the natural residual soils are acidic and of low fertility, needing the addition of lime, potash and superphosphates. Given intensive labour input, however, water supply rather than soil condi- tion tends to be the controlling factor in farming. The predominantly crystalline character of the rock formations unfortunately makes them unsuitable as aquifers for underground storage and this makes it necessary to concentrate on the collection of surface run-off for all water supplies. The highly variable rainfall of the area has led to periodic water shortages. Most of the Colony's surface water supply has now been captured through the construction of catch- ments and reservoirs, and with the completion of the High Island reservoir scheme, desalination processes on a large scale will prob- ably become necessary.
Hong Kong lies in the frost-free double-cropping rice zone of East Asia, but more profitable crops have increasingly displaced rice during the past 25 years and it is now grown on only 40 per cent of the area being used for agriculture. Intensive market garden- ing, principally for vegetables and with associated pig and poultry raising, is the most important agricultural activity. Vegetables are grown throughout the year-as many as eight or 10 crops from a single patch—but most particularly during the cooler months. Fish ponds are also an important form of rural land use. The upland areas are mostly grass-covered and in several places, as in the Castle Peak area, severely eroded. Afforestation has been developed since 1945 but the area covered is still relatively small. The most important function of the uplands is for water catchment areas. To some extent this is now conflicting with the needs of the crowded urban areas for recreational space, and problems of rural conservation in this and other respects are becoming pressing.
CLIMATE
Although Hong Kong lies within the tropics it enjoys seasonal weather conditions, which is unusual for tropical countries. The winter monsoon blows from the north or north-east and normally begins during September. It prevails from October until mid-March but can persist until May. Early winter is the most pleasant time of