Geology of Mount Sinai and adjacent Countries. 263 



felspar, spotted green with hornblende. Some varieties 

 would pass for diallage in hand specimens, though the rock 

 has an obscurely stratified structure. Its weathered exterior 

 has a dark rusty colour." 



Burckhardt observes the porphyry of the Sinai district is 

 usually red ; in some specimens it has the appearance of red 

 felspar. In others are imbedded small crystals of hornblende, 

 or of mica, and thin pieces of quartz. But, at the spring 

 Tabakat, near Gebel-um-Schomar, he discovered a beautiful 

 porphyry having large slabs oi felspar, traversed by veins of 

 rvhite and rose quartz. The same traveller describes the 

 white granite of the summit of that lofty mountain, as appear- 

 ing at a distance like chalk ; this he accounts for from a 

 great quantity of rvhite felspar in it, and from the smallness 

 of the particles of hornblende and mica. He adds, the quartz 

 also in it is of a brilliant whiteness. 



The following particulars relative to some other varieties 

 of rocks, are collected from Dr Kitto's work.* 



A specimen from the Sinaic peninsula, figured in a plate of 

 the "Description de I'Egypte," is named by M. de Roziere, 

 talcose quartz ; it is said to form extensive beds towards the 

 middle of the route which leads from Gebel Mousa to Ras 

 Mohammed. This quartz offers certain slight lamellar ap- 

 pearances, and in some of the varieties felspar is associated 

 with it. The rocks wherein the quartz most prevails, " divide 

 themselves into cruciform fragments, the greenish surfaces 

 of which clouded with red and yellow, are ornamented with 

 beautiful, dark, and thickly tufted dendrites. ^^ 



The summit of Gebel Katherin, composed of a variety of 

 Sina'ite, differs by its clear colour and neat crystallization 

 from the coarser porphyritic and Sinai tic rocks that consti- 

 tute the chief part of that mountain. The crystallization of 

 the felspar in the Sinaite of the adjoining top of Gebel Mousa 

 is more confused, the crystals of hornblende are less, and 

 those of quartz are more numerous, but also smaller than in 

 the other ; mica is absent in both of these. 



* Sec Phys Geogr. of iho Holy fjand, chap. 2. 



