To the south of the ancient mining district the sandstone is connected in a manner highly interesting to the geologist with the plutonic rock which gives its imposing character to the mountains of the south. Here lies the Wadi Feiran, one of the best watered and fruitful valleys of the peninsula, to the south of which Mount Serbal rises abruptly from a comparatively low elevation to the height of 6734 ft. This mountain has been described as one great lump of diorite, and its majestic appearance led some recent travellers, including Lepsius[2] and Bartlett,[3] to identify it as the Mountain of the Law. Further south lies the great group of mountains which include the Gebel Musa, 7359 ft. high, and the Gebel Katrîn with its three peaks, the highest of which rises to 8527 ft. The Gebel Musa from early Christian times was generally looked upon as the Mountain of the Law. At its foot lies the great convent of Sinai, at one time known as the Bush, which has carried on to the present day the traditions of the early Christian hermits, who settled in the peninsula. The Gebel Katrîn lying further south, was looked upon during the later Middle Ages, as the height on which the angels deposited the body of St. Katherine. Another imposing height of the group is the Ras Safsaf, 6540 ft. high, which has been put forward in recent times as a possible Mountain of the Law. These mountains of the south contain many natural springs and fruitful valleys, which were formerly the home of Christian ascetics. They are divided from the Gulf of Suez on the west by the desert of El Kaa, which drains a large amphitheatre of hills, and becomes a coastal plain that extends as far as Ras Mohammad, the southernmost point of the peninsula. The desert of El Kaa has a harder subsoil which is so tilled that the accumulated moisture is thrown up at the coast near Tur, the chief harbour of the peninsula, and possibly an ancient Phœnician colony. Near it lay Raithou, a place of many oases and large date-palm plantations which were carefully tended by the monks during the Middle Ages.