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Tunnels of Gibraltar
The tunnels of Gibraltar, constructed over the course of nearly 200 years principally by the British Army, have made the Rock of Gibraltar "a veritable warren of tunnels that housed guns, hangars, ammunition stores, barracks and hospitals".〔Fa & Finlayson, p. 6〕 Within a land area of only , Gibraltar has around of tunnels, nearly twice the length of its entire road network. The first tunnels, excavated in the late 18th century, served as communication passages between artillery positions and housed guns within embrasures cut into the North Face of the Rock. More tunnels were constructed in the 19th century to allow easier access to remote areas of Gibraltar and accommodate stores and reservoirs to deliver the water supply of Gibraltar.
The 20th century saw by far the greatest extent of tunnelling when the Rock was turned into a huge underground fortress capable of accommodating 16,000 men along with all the supplies, ammunition and equipment needed to withstand a prolonged siege. The tunnelling finally ceased in 1968 when the British Army's last specialist tunnelling unit was disbanded. Since then, the tunnels have progressively been turned over to the civilian Government of Gibraltar, although a number are still owned by the Ministry of Defence and some have been sealed off entirely as they are now too dangerous to enter.
==Geology of Gibraltar==
The Rock of Gibraltar is interpreted by geologists as a klippe of Jurassic dolomitic limestone with series of 'shale' formations underlying and in part overlaying the limestone.〔Rose (2000), p. 244〕 It consists primarily of a series of carbonate deposits some thick, varying from dark grey bituminous dolomite at the base through to a very thick, apparently homogeneous sequence of light or medium grey fine-grained limestones. The formation appears to have been laid down in a tropical environment somewhat similar to the Bahamas today, and on the basis of fossil evidence an Early Jurassic (Sinemurian) age has been proposed for the Gibraltar Limestone, though in appearance it has a strong resemblance to the Carboniferous Limestone that underlies large parts of England and Wales.〔〔
The formation's thick bedding, extensive cementation and dolomitisation have made it a generally stable engineering material.〔Rose (2001), pp. 99–100〕 Tunnelling has been possible almost throughout the Rock, with the exception of one region where it has been precluded due to high ground water pressures. In some areas, zones of weak rock or intrusions of the underlying or overlying 'shales' have caused tunnel instability.〔Rose (2000), p. 259〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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