The Rock of Gibraltar is a monolithic limestone mountain 426 m (1,398 ft) high dominating the western entrance to the Mediterranean Sea at the Strait of Gibraltar. It is situated near the end of a narrow 9-kilometre-long (5.6 mi) promontory stretching due south into the Mediterranean Sea and is located within the British territory of Gibraltar. The rock is 27 km northeast of Tarifa, Spain, the southwestern tip of Europe on the Iberian Peninsula. The rock serves as a fortress and contains a labyrinthine network of man-made tunnels known as the Tunnels of Gibraltar. Most of the Rock's upper area comprises a nature reserve which is home to about 300 Barbary macaques. It is a major tourist attraction. The Rock of Gibraltar, the northern of the two historic Pillars of Hercules, was known to the Romans as Mons Calpe ("Mount Calpe"); the southern Pillar of Hercules on the African side of the Strait of Gibraltar was known as Mons Abila, with a modern name of either Monte Hacho or Jebel Musa. According to an ancient legend fostered by the Greeks and the Phoenicians and later adopted by the Romans, the two pillars marked the western limit of the known world.
Geology
The Rock of Gibraltar is a monolithic promontory. The Main Ridge has a sharp crest with peaks over 400 metres (1,300 ft) above sea level, formed by Early Jurassic limestones and dolomites. It is a deeply eroded and highly faulted limb of an overturned fold. The sedimentary strata composing the Rock of Gibraltar are overturned, with the oldest strata overlying the youngest strata. These strata are the Catalan Bay Shale Formation (youngest), Gibraltar Limestone, Little Bay Shale Formation (oldest), and Dockyard Shale Formation (age unknown). These strata are noticeably faulted and deformed. Predominantly of shale, the Catalan Bay Shale Formation also contains thick units composed of either brown calcareous sandstone, soft shaly sandstone interbedded with bluish-black limestone, and interlayered greenish-gray marls and dark grey cherts. The Catalan Bay Shale Formation contains unidentifiable echinoid spines and belemnite fragments and infrequent Early Jurassic (Middle Lias) ammonites. The Gibraltar limestone consists of greyish-white or pale-gray compact, and sometime finely crystalline, medium to thick bedded limestones and dolomites that locally contain chert seams. This formation comprises about three-quarters of the Rock of Gibraltar. Geologists have found various poorly preserved and badly eroded and rolled marine fossils within it. The fossils found in the Gibraltar limestone include various brachiopods, corals, echinoid fragments, gastropods, pelecypods, and stromatolites. These fossils indicate an Early Jurassic age (Lower Lias) for the deposition of the Gibraltar limestone. The Little Bay and Dockyard shale formations form a very minor part of the Rock of Gibraltar. The Little Bay Shale Formation consists of dark bluish-gray, unfossiliferous shale, which is interbedded with thin layers of grit, mudstone, and limestone. It predates the Gibraltar limestone. The Dockyard Shale Formation is an undescribed variegated shale of unknown age that lies buried beneath the Gibraltar's dockyard and coastal protection structures. Although these geological formations were deposited during the early part of the Jurassic Period some 175–200 million years ago, their modern appearance is due to events of about 5 million years ago. When the African tectonic plate collided tightly with the Eurasian Plate, the Mediterranean became a lake that, over the course of time, dried up during the Messinian salinity crisis. The Atlantic Ocean then broke through the Strait of Gibraltar, and the resultant flooding created the Mediterranean Sea. The Rock forms part of the Betic Cordillera, a mountain range that dominates southeastern Iberia. The local geology of the region has been uplifting the rock at roughly 0.05 mm (0.0020 in) per year for the past 200,000 years (or a total uplift of around 10 metres or 33 feet), and for at least 50,000 years before that had been uplifted by 0.33 mm (0.013 in) per year for a combined uplift of about 26.5 metres (87 ft) in the past 250,000 years.
The Rock of Gibraltar forms a peninsula jutting out into the Strait of Gibraltar from the southern coast of Spain. The promontory is linked to the continent by means of a sandy tombolo with a maximum elevation of 3 m (9.8 ft). To the north, the Rock rises vertically from sea level up to 411.5 m (1,350 ft) at Rock Gun Battery. The Rock's highest point stands 426 m (1,398 ft) near the south end above the strait at O'Hara's Battery. The Rock's central peak, Signal Hill and the top station of the Gibraltar Cable Car, stands at an elevation of 387 m (1,270 ft). The near-cliffs along the eastern side of the Rock drop down to a series of wind-blown sand slopes that date to the glaciations when sea levels were lower, and a sandy plain extended east from the base of the Rock. The western face, where the City of Gibraltar is located, is comparatively less steep. Calcite, the mineral that makes up limestone, dissolves slowly in rainwater. Over time, this process can form caves. For this reason the Rock of Gibraltar contains over 100 caves. St. Michael's Cave, located halfway up the western slope of the Rock, is the most prominent and is a popular tourist attraction. Fossils of Neanderthals have been found at several sites in Gibraltar. In 1848, a Neanderthal woman's skull was found at Forbes' Quarry, located on the north face of the Rock. However, its significance was not recognised until after the 1856 discovery of the type specimen in the Neander Valley. Excavations in Gorham's Cave, located near sea level on the eastern side of the Rock, found evidence it was used by Neanderthals, and plant and animal remains in the cave gave evidence of Neanderthals' highly varied diet.
Eastern face
The Eastern Face of the Rock comprises steep cliffs and scree slopes descending to the sea, allowing little space for human habitation. In modern times a road (Sir Herbert Miles Road, named after Lieutenant General Sir Herbert Miles, Governor of Gibraltar 1913–1918) has been cut into the shore, its southernmost part being through a tunnel (Dudley Ward Way, named after Sir Alfred Dudley Ward, Governor of Gibraltar 1962–1965) in the rock. Towards the south-east end of the Rock close to sea-level is located Gorham's Cave, a UNESCO World Heritage Site.
Fortification
Moorish castle
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