GEOLOGY OF MAROCCO AND GREAT ATLAS. 461 



mounds in the valley west of Tasseremout at once conveyed to 

 me the impression that they were of glncial origin ; and the 

 discovery of undoubted moraines in the higher valleys strength- 

 ened my conviction that the boulder-mounds and ridges flanking 

 the Atlas plateau can only be satisfactorily explained as the 

 result of glaciers covering the escarpment, leaving on their re- 

 cession the intermediate depression. 



(b) Moraines of the Higher Atlas. — Kindred phenomena 

 occur higher up in the Atlas valleys, most notable in the case 

 of unquestionable moraines, commencing at the village of Ad- 

 jersiman, in the province of Eeraya, at an altitude of 6,000 feet. 

 Here we met with a gigantic ridge of porphyry blocks, having 

 a terminal angle of repose of between 800 and 900 feet in 

 vertical height, and grouped with several other mounds and 

 ridges of similar scale, all composed of great masses of rock with 

 little or no admixture of small fragments, and completely 

 damming up the steep ravine and retaining behind it a small 

 alluvial plain 6,700 feet above the sea-level. 



We failed to detect any scratched blocks or striae ; but that 

 these ridges are true glacial moraines no one who has seen them 

 and compared them with other glacial phenomena would for 

 a moment doubt ; and their interrupted occurrence at various 

 heights is strictly in accordance with the distribution of mo- 

 raines in many of the Swiss and Scotch valleys. 



Lieut. Washington, in referring to the pointed mountainous 

 hUls NW. of the city of Marocco, crossed on his homeward 

 journey, describes one of them as being ' covered with masses of 

 gneiss and coarse-grained granite (? diorite), many of the blocks 

 being several tons in weight,' and asks, ' how got they there 1 ' ' 

 ' If granite, the nearest granite mountaias are at a distance of 

 twenty-five to thirty miles : can they be boulders 1 ' As far as 

 my own observations go, there was no rock in situ in the part 

 of this range I visited near Marocco resembling granite or dio- 

 rite ; and in connection with the boulder-mounds of the Atlas, 

 the occurrence of foreign blocks north of the plain of Marocco 

 so far from the parent source, is a circumstance of great interest. 



(c) Stratified Red Sandstone and Limestone Series. — A long 

 line of comparatively low and flattish hills, forming a plateau, 

 with an average height of about 4,500 feet above the sea, and 

 2,800 feet above the plain of Marocco, intervenes between it 



