210 JOSEPH THOMSON ON THE GEOLOGY OF [May 1 899, 



considerable thickness of diorite is seen to have been intruded 

 between the Cretaceous strata. Farther up still occurs a con- 

 formable bed of volcanic breccia ; and then, at the point where 

 the Wad Agandice branches into two, is a great intercalated sheet 

 of basalt. Whether this is a contemporaneous lava-sheet, or sub- 

 sequently intruded between the beds, I cannot say, but incline to the 

 former view. In any case, it can be traced in a conformable sheet 

 right up to the top of the mountain which overlooks the Wad Sus, 

 on the south side of the Atlas range. 



In returning to the plain, the way lies down the Wad N"vfis, 

 instead of across the mountains. On leaving Gindafy, the traveller 

 passes at first through a narrow gorge cut out of the sandstones, 

 here hardened and altered. From the sandstones he quickly passes 

 to the friable, much- jointed, and thinly-bedded schists of the meta- 

 morphic area, with a corresponding broadening of the gorge into a 

 tortuous glen, its many windings being due to the occurrence at 

 places of more compact rocks. These schists and grauwackes mark 

 the whole course of the Nyfis, till near the mouth of the glen, where 

 some red sandstones and shales reappear. 



The chief point of geological interest that calls for attention in 

 the glen of the Wad Nyfis is the undoubted evidence of glacial 

 action which may be remarked at several localities. Heaps of 

 moraine-debris are to be seen at various elevations above the river- 

 channel, and among the boulders I met with several well-striated 

 specimens. Further evidence of glaciation is to be found in the 

 smoothed and polished rock-surfaces, which have been preserved from 

 the destructive effects of frost and rain by a covering of glacial 

 debris. 



(7) The Asi£ el Mel. (Fig. 6, p. 208.) 



In the section across the small province of Marossa and Jebel 

 Ogdimt to Sus one finds a comparatively much greater development 

 of the metamorphic area than in the section that has just been 

 considered. In its main features it resembles the section displayed 

 in the glen of the Wad Demnat (p. 199). Thus, a thin series of 

 yellowish limestones and sandstones are seen clinging in vertical 

 beds to the outer flank of the Atlas range, and resting against the 

 metamorphic schists, which rise into low, broken mountain-masses, 

 A few miles up the glen, a capping of Cretaceous rocks of con- 

 siderable thickness appears, dipping very slightly southward and 

 ending abruptly against the western continuation of the fault already 

 remarked in the Amsmiz glen (p. 207). Here also the metamorphic 

 rocks shoot up from beneath the sandstones, and rise into picturesque 

 mountain-masses with stern, precipitous faces. There is one point to 

 be noted in our examination of this fault — namely, the clear evidence 

 which it presents that the upheaval of the Atlas range has not 

 been solely due to the mere folding of the earth's crust, but that 

 the main force or chief line of weakness lay along the central axis 

 of the mountains ; and that, in consequence, the internal parts 



