22 J. MILNE ON THE SINATTIC PENINSULA AND N.W. ARABIA. 



3. Basalt from the exterior of a dyke, of which. No. 4 is the interior. This 



is a compact and almost black, eyen-textured roc;k, and is slightly 

 calcareous. 



4. Dolerite, much degraded, from the interior of a dyke, of which No. 3 is 



the exterior. This is a greenish grey, loose-textured, granular rock, 

 which is decidedly calcareous and also magnetic. 



5. Pinkish granite, through which the above dyke3 penetrate. 



6. Porphyry, red crystals in a green base. 



7. Porphyry, of a greyish colour, containing acicular crystals of hornblende. 



8. Porphyry like No. 7, but with large crystals of hornblende. 



9. Porphyry, a compact felsitic mass. 



10. Porphyry, darker-coloured than No. 9. 



11. Porphyry, fine-grained and of a lavender colour. 



Geological Formations. — "When on the top of Mount Baghir, on look- 

 ing from the north, by the east, round to the south-east, flat-topped 

 hills were seen which from their shape were at once suspected not 

 to be granitic, or, if granitic, to be capped by some other material. 

 This conjecture was confirmed by visiting the top of Mount Atagta- 

 gheer, on the summit of which there are two large patches of sand- 

 stone, each about 100 feet in thickness, which have apparently been 

 deposited subsequently to the formation of the granite. The beds, 

 which are nearly horizontal, have a parallelism with the gentle 

 undulations of what appears to be the denuded surface of the 

 granite on which they rest. In no place does the granite appear to 

 penetrate into the beds above, or in any way to break their even 

 line of stratification ; nor, on the other hand, does the sandstone 

 descend into any crevices or irregularly eroded cavities in the 

 granite. The lower beds of this sandstone, which are about 3000 

 feet above sea-level, are composed of a coarse quartzose material very 

 like that which would be derived from granite after the washing 

 away of the lighter materials. The remaining beds higher up, with 

 the exception of a bed near the summit, which is of a perfectly 

 white, fine-grained, soft sandstone, are composed of a yellowish gritty 

 sandstone. 



Although carefully looked for, no organic remains were to be 

 found. Scattered over the top of the mountain were some com- 

 pact dark-coloured rocks, probably the remains of a dyke cutting 

 through some neighbouring mountain from which they have been 

 derived. 



To the east and north of this mountain there were many flat- 

 topped hills ; and the beds, which here only formed caps, appeared 

 in the distance to form the hills themselves, the cliff-like faces of 

 which showed curious barrel-shaped outlines. This same formation, 

 resting on the granite, is to be seen at the head of Wady Amran, 

 where it stretches away eastwards towards the centre of Arabia, 

 and southwards towards the somewhat similar beds which were 

 seen at Madian. 



It has been asserted, on very good grounds, that in this portion 

 of Arabia there are still remaining evidences of several once active 

 volcanoes. Should these be discovered, they will in all probability 

 be found amongst the sandstones on the eastern side of the great 

 Arabian watershed ; for had they existed on the western side, some 



