plates slide towards each other forming a subduction zone (if one plate moves underneath the other), and/or a continental collision (when the two plates contain continental crust). In the case of the Africa-Europe collision, it is clear that tectonic convergence is partially responsible for the formation of the High Atlas, as well as for the closure of the Strait of Gibraltar and the formation of the Alps and the Pyrenees. However, there is a lack of evidence for the nature of the subduction in the Atlas region, or for the thickening of the Earth's crust generally associated with continental collisions. In fact, one of the most striking features of the Atlas to geologists is the relative small amount of crustal thickening and tectonic shortening despite the important altitude of the mountain range. Recent studies suggest that deep processes rooted in the Earth's mantle may have contributed to the uplift of the High and Middle Atlas. Natural resources The Atlas are rich in natural resources. There are deposits of iron ore, lead ore, copper, silver, mercury, rock salt, phosphate, marble, anthracite coal and natural gas among other resources. Subranges The range can be divided into four general regions: Anti-Atlas, High Atlas and Middle Atlas (Morocco) Tell Atlas (Morocco, Algeria, Tunisia) Aurès Mountains (Algeria, Tunisia) Saharan Atlas (Algeria) Anti-Atlas The Anti-Atlas extends from the Atlantic Ocean in , the southwest of Morocco toward the northeast to the heights of Ouarzazate and further east to the city of Tafilalt (altogether a distance of approximately ). In the south it borders the Sahara. The easternmost point of the anti-Atlas is the Jbel Saghro range and its northern boundary is flanked by sections of the High Atlas range. It includes the Djebel Siroua, a massif of volcanic origin with the highest summit of the range at 3,304 m. The Jebel Bani is a much lower range running along the southern side of the Anti Atlas. High Atlas The High Atlas in central Morocco rises in the west at the Atlantic coast and stretches in an eastern direction to the Moroccan-Algerian border. It has several peaks over , including the highest summit in North Africa, Toubkal (), and further east Ighil m'Goun (), the second major summit of the range. At the Atlantic and to the southwest, the range drops abruptly and makes a transition to the coast and the Anti-Atlas range. To the north, in