20 J. MILNE ON THE SINAITIC PENINSULA AND N.W. AEABIA. 



be now represented by small caves, one of which was about 20 feet 

 in diameter and 10 or 12 feet in height at its entrance, sloping down 

 with a dome-shaped roof and curved sides towards the back. No 

 angular forms are visible, which shows that the granite has flaked 

 off in curved laminae. On striking this rock with a hammer it has not 

 the clear ring of a solid stone, but gives a dull sound, owing to the 

 surface being so disintegrated and having the tendency to split off 

 in flakes, which can easily be separated with the sharp edge of the 

 hammer. 



The peaks on the summit of this mountain are composed of 

 granite ; the hollows between them mark the position and direction 

 in which the mass is traversed by dykes ; and it may be stated 

 as a general rule for this mountain, that the dykes do not protrude 

 above the granite, but all tend to produce hollows. One exception 

 to this, however, was seen on the N\E. side of the mountain, near a 

 well, where a dyke formed a clearly defined ridge running up towards 

 the summit. These dykes, which are generally of a dark green 

 colour, vary in width from 1 foot to 18 feet, and perhaps more. 

 When struck with a hammer, in many places they appear to be 

 quite earthy, crumbling up like dry clay. The general direction 

 of these and others in the neighbouring mountains is from between 

 north and east to some point between south and west, often striking 

 in long parallel lines across ridges of the hills. 



Eocks from Jebel Baghir (Sinai) (the first three of these were 

 examined microscopically) : — 



1. Dolerite, much decomposed, of a dark colour, loose texture, and a greyish 



exterior, owing to the weathering of the felspar. 



2. Dolerite, portion of a compact, hard nodule, taken from the interior of 



the dyke of which No. 1 formed part. 



3. Diabase, passing from porphyritic to aphanitic. The rock is black and 



dense ; no structure is observable. 



4. Granulitic granite, a fine-grained mixture of quartz and felspar, with 



finely distributed mica. 



5. Granite, fine-grained and pinkish. 



6. Mica and felspar, with very little hornblende, the whole forming an 



irregular greenish mass." 



7. Granite, of a pinkish colour. 



8. Granite, nearly all felspar. 



Dykes. — The prominent part taken by dykes in giving the character- 

 istic ruggedness to these granite hills has already been partially noted, 

 as will be seen from the following observations of Dr. Oscar Praas, 

 ' Aus dem Orient/ where, at page 15, he says, " When on the 

 summit of Serbal, in a circuit of about 1000 metres, rather more 

 than less, I counted from our pinnacle 47 peaks, or, as might be 

 plainly seen from those which were nearest to us, so many dykes of 

 diorite which stood above the mass of granite. In the conrse of 

 the incalculable ages during which these points had been exposed 

 to the atmosphere, they had offered a different resistance to the 

 weathering than had the granite with its felspars ; and therefore as 

 many diorite teeth stood out from the granite bed of Serbal as 

 you could count points on the mountain." 



