ENG-2009 — Page 359

The Environment 287

dedicated to conservation, education and scientific studies. Fishing in marine parks is controlled through a permit system while such activity is totally banned in marine reserves. Publicity and educational activities are organised for students and members of the public.

Besides designating protected areas, the Government has been identifying and conserving sites of special scientific interest (SSSI), such as areas with special geological features and natural habitats of rare plants or animals, by exercising strict. land use planning and development controls. There are 67 sites listed in the SSSI register.

Topography and Geology

Hong Kong's natural terrain is characterised by rugged uplands flanked by steep slopes. The highest point is Tai Mo Shan (957 metres above Principal Datum) in the central New Territories, and the lowest point (66 metres below Principal Datum) is in Lo Chau Mun (the Beaufort Channel) to the north of Po Toi Island. The mountains are predominantly formed of volcanic rocks, whereas the lower hills consist mainly of granite. Low-lying areas are generally underlain by granite or sedimentary rocks. A layer of soft, weathered rock covers the bedrock in most places, slope debris mantles the natural hillsides, and alluvium fills many of the valleys. Offshore, the seabed is covered with marine mud, with sand sheets occurring near the coast and in channels.

The oldest exposed rocks in Hong Kong are composed of Devonian river sediments that were deposited approximately 400 million years ago. The region was subsequently inundated by a shallow sea, which deposited Carboniferous limestones, the parent material of the Yuen Long and Ma On Shan marble. Between 170 to 140 million years ago, during the Jurassic and Cretaceous periods, violent volcanic eruptions were associated with deposition of thick ash and lava layers and the development of several calderas (giant craters). At deeper levels, molten magma was intruded and slowly crystallised to form granite. Layered rocks now seen on the island of Ping Chau are younger sediments, laid down in a lake on the edge of a desert, about 55 million years ago.

During the last 2.6 million years, the Quaternary Period, major glaciations caused successive lowering of world sea level of up to 120 metres, which resulted in the coastline being about 120 kilometres to the south. During interglacial periods, such as the present time, global sea level rose and marine sediments were deposited.

A series of fifteen 1:20 000-scale geological maps and six accompanying geological memoirs have been produced by the Hong Kong Geological Survey, a part of the Geotechnical Engineering Office. The Hong Kong Geological Survey has also published two summary memoirs and a set of 1:100 000-scale geological and thematic maps that synthesise the geology of Hong Kong. A popular account of the geology of Hong Kong, in Chinese and English, has also recently been published. Detailed geological information is available at the website of the Civil Engineering and Development Department.