460 APPENDIX H. 



which, terminate at a well-marked line of demarcation, just 

 where the level portion of the plain commences. I measm-ed 

 by aneroid the height of these mounds ; and at one point their 

 summit was 3,950 feet above the sea-level, from which they 

 spread down uninterriiptedly to the edge of the plain nearly 

 2,000 feet below. They bear a striking resemblance to the 

 glacial ridges or esoars between Edinburgh and Perth ; their 

 mound-like structure is distinctly visible from the city of Ma- 

 rocco, twenty-five miles off, appearing like a row of pyramidal 

 tali resting against the face of the escarpment as though they 

 had been cast down from its edge on to the plain. The internal 

 structure of the mounds also suggests such a deviation from the 



Boulder-mounds, skixLing Atlas Plateau Escarpment. 



disposition of the boulders in layers sloping away from the es- 

 carpment towards the plain ; and on a nearer approach it is seen 

 that the individual mounds are not connected with channels or 

 valleys breaking through the escarpment. 



The depression between the escarpment and the drift- 

 mounds is a remarkable feature, and suggests an entire change 

 of conditions since the boulder-beds were deposited. If they 

 are a mere sub-aerial talus, they should rest directly against the 

 cliff face, and the depression separating them must have been 

 formed after the accumulation had ceased ; and yet no satis- 

 factory reason can be assigned for such cessation, if rain and 

 river action were the only operating causes. The form of the 



