Yol. 55.] SOTJTHEEN" MOEOCCO AND THE ATLAS MOUNTAINS. 199 



both sides of the range, and, north of Jebel Glauwa, completely 

 masking them. This series may be found at a height of over 

 11,000 feet above sea-level on either side of the Tizi-n-Teluet» 

 rhirdly, there is a less conspicuous development of the Limestone 

 Series, flanking only the outer and lower elevations of the range, and 

 probably never rising to a greater elevation than 5500 feet. This 

 series (in the mountains) is characterized by the numerous basalt- 

 dykes which break through it, with a general trend parallel to the 

 main axis of the chain. In the fourth place, though no clear proof 

 is forthcoming that any of the coastal Tertiary rocks are repre- 

 sented, there is undoubted evidence of a Glacial period in the later 

 history of the mountains, in the shape of moraine-heaps and ice- 

 worn rocks and boulders in their glens and valleys. 



Where so little is known, every observation has a certain value ; 

 and therefore, instead of considering each formation separately, I 

 think that the best plan will be to act as guide to each glen, and take 

 such note of the section exposed therein as the circumstances of 

 the case will permit. The diagrammatic sections which 1 have 

 prepared (figs. 1-6) will aid in the elucidation of my remarks. 



I propose to commence at Demnat, taking the glens in their 

 order westward :— 



(1) The Wad Demnat. (Fig. 1, p. 200.) 



The Wad Demnat leaves the Atlas Mountains near the eastern 

 termination of the great plain of Morocco. The entrance to the glen 

 is through an open gorge cut out of a series of vertical limestones 

 with intercalated beds of shale. The glen speedily begins to open 

 out, the widening being due to a great dyke or boss of easily 

 weathered basalt, the occurrence of which provides a clue to the 

 origin of the vertical position of the limestones and the unusual 

 fertility of the soil. The town of Demnat stands in the hollow 

 formed by the denudation of the basalt, the limestone-rocks sur- 

 rounding it in an irregular amphitheatre of mountains and hills. 

 Proceeding up the beautiful, fertile, terraced valley, the mountains 

 close in, as the traveller passes once more from the basalt to the 

 compact Limestone Series. This is not, however, thrust up verti- 

 cally, but dips south or towards the mountains at an angle of 

 some 30°. From this point the sides of the glen rapidly close in 

 till, about 3 miles sonth of the town, they meet, seemingly blocking 

 the valley by a precipice between 150 and 200 feet high, from the 

 top of which the mountains again spring to a further height of 

 500 to 1000 feet. 



At first the Wad Demnat appears to well from the living rock at 

 the base of the limestones, but further observation reveals the 

 existence of a narrow, broken gorge, arched over by a natural 

 bridge of travertine, which joins the walls of the gorge at an 

 altitude of over lOO feet. More remarkable still, it soon appears 

 that this natural bridge fulfils the function of an aqueduct, by 

 which a considerable stream is conveyed from one side of the glen 



