[Illustration: Fig. 9.—Granite-porphyry, Kreishim Hill [12,150], viewed between crossed nicols, × 10. _q_, quartz (the dark triangular area to the left of figure is also a quartz crystal in the position of extinction); _f_, felspar (oligoclase); _g_, micro-granitic ground mass.] Under this heading are comprised rocks of granitic composition in which porphyritic crystals of quartz, felspar, and mica are surrounded by a fine-grained ground mass of entirely granitic (holocrystalline) character. They differ from porphyritic granites in the much finer grain of the general body of the rock, and from the quartz felsites in the entire absence of glassy matter from the ground mass. Rocks of this type are scarce in South-Eastern Egypt. An example [12,150] occurs at the hill called Kreishim, sixteen kilometres west of Halaib. Here the rock, which appears to form a small boss, consists of rounded white porphyritic crystals set in a finely crystalline grey ground mass. The sp. gr. is 2·69. Under the microscope (Fig. 9) the porphyritic crystals are seen to consist of quartz and oligoclase, the latter in approximately idiomorphic crystals, often beautifully zoned; the ground mass, of micro-granitic structure, is made up of smaller allotriomorphic crystals of quartz, felspar, and biotite. Dykes of granite-porphyry also occur traversing the granite of Gebel Kahfa [11,537 B] and in the basic rocks of Gebel Um Bisilla [11,518]. At both these places the rocks are far less fresh than that above described. In the hand specimen they are of a greyish-white or greenish-white colour, strongly resembling fine-grained aplites in appearance. With the lens, crystals of quartz and felspar can be made out, and specks of hornblende and chlorite. The microscopic slides show the characteristic structure of granite porphyry, but the felspars are all clouded by decomposition products, and the hornblende, which is rather sparingly present in the ground mass, is mostly changed to chlorite and epidote. The specimen from Gebel Kahfa contains a small amount of muscovite. =Quartz-felsite.= Though covering only small areas, quartz-felsite is of very wide distribution in South-Eastern Egypt. It typically forms dykes and intrusive sheets traversing the plutonic and metamorphic rocks, but likewise occurs occasionally in larger masses. Felsite dykes are specially abundant in the neighbourhood of Gebels Muelih, Zergat Naam, and Um Reit. Larger masses occur in the Wadi Huluz, and form the summits of Gebels Nigrub el Foqani and Hamata.