26 J. MILNE ON THE SINAITIC PENINSULA AND N.W. ARABIA. 



ridges on the right, through which occasional glimpses of the great pla- 

 teau of the Tih are to be seen, continues for nearly a day's journey. 



After passing Jebel Duppa the ranges on the right, growing higher, 

 show a more definite character as compared with those upon the 

 left. Whilst the latter remain horizontal, the former are almost 

 turned on end, dipping at an angle of 45° to the north. They 

 consist of limestones which are whitish at their base and yellowish 

 near their summit. With them there are bands of flint, which, 

 being tilted up with the rock in which they are stratified, stand 

 up along the ridges of the hills, forming low parallel walls 

 to hollow troughs. Numerous angular and apparently freshly 

 broken fragments of these flints are strewn over the plain below, 

 apparently broken by the more or less sudden expansion and con- 

 traction occasioned by the great variations in temperature, this 

 action being probably aided by a jointed structure in the flint at the 

 time of its removal from the limestone. That there are such 

 variations in temperature may be inferred from the fact that many 

 nights when we were in the desert the thermometer sank below 

 zero, and shrubs and other objects were in the morning covered with 

 a thick coating of hoar frost, this low temperature being invari- 

 ably followed shortly after sunrise by a heat that readily scorched 

 and peeled the skin from the face. 



In addition to this it may be mentioned that several rounded and 

 apparently whole flints were seen, which, on being touched, fell to 

 pieces, showing them to have been broken by some force that had 

 not been violent in its action, but had simply divided them and not 

 scattered the fragments. 



Materials being in this way continually supplied from a mountain, 

 then being broken by the sun and afterwards buried in the sand, 

 may perhaps give a clue to the origin of certain breccias. 



At the western end of this range there is a large and well- 

 defined wady stretching away to the north-west into a low undu- 

 lating country of chalk-like rocks. At the entrance to this there 

 is a small, solitary hill of chalk resembling an island, and showing 

 the steep northern dip which characterizes the rocks along the 

 southern side of this portion of the Hadj road. 



At less than a mile past this a cutting has been made through a 

 hill composed of fine-grained and perfectly white chalk, which gives 

 a small but clear section of this rock, showing on its walls and also 

 in the ground over which you walk, a great continuity of bands of 

 flint 



Looking at the upturned edges of these bands upon the floor of 

 the cutting, in places they are seen to have been divided and then 

 reunited, forming cavities which are filled with a material in ap- 

 pearance like the surrounding rock. At several points along the 

 walls of these cuttings numerous irregular, coral-like concretions 

 stand out, through the weathering away of the softer material which 

 once surrounded them. 



On the left-hand side of the road it appeared as if the upturned 

 chalky strata just referred to abutted against the horizontal yellow 



