194 JOSEPH THOMSON ON THE GEOLOGT OF [May 1 899, 



of the Wad Misfiwa, I penetrated the glens of the streams described, 

 and was thus able, thanks to the sections displayed in their precipices 

 and bare rocky slopes, to form a very fair idea of the internal 

 structure and constitution of the range, despite the difficulties which 

 beset me on every hand. 



As regards the southern slopes, I need say but little : from Agadir 

 to the borders of the province of Glauwa the Wad Sus collects all the 

 ■drainage, while farther east the Draa performs that function. 



In possession of these general notions regarding the geography of 

 Southern Morocco and its great mountain-chain, one may now more 

 intelligibly proceed to consider the internal structure of the region. 



III. The Coastal Loavlands. 



Commencing this survey with the coastal lowlands, I may re- 

 mark that they are practically conterminous with the Tertiary 

 deposits, which here attain a very considerable development. 



At Casablanca they form a vast plain, but little raised above the 

 level of the sea, and consisting of grey and puce-coloured shales, 

 which probably, judging from lithological resemblances, belong to 

 the same series as the Cretaceous rocks around Tangier. 



Travelling southward, the country rapidly rises to a height of 

 100 or more feet, and stretches out in undulating treeless monokfcony. 

 Here one remarks flaggy sandstone, which farther on disappears. 

 At Azimur the cliif-sections of the Um-er-Eebia show a series of 

 reddish friable rocks and porous conglomerate, with shell-rock at 

 the top. The lower of these have been regarded as Eocene, and 

 the upper as Miocene — from the occurrence of Teredina personata 

 in the one, and Balanus sulcatus, Pecten Beudanti, Area, Buccinum 

 prismaticum, and Conus in the other.^ 



Prom Mazagan to the south of Azimur my route led inland 

 through the provinces of Dukalla and Abda, and as there were 

 neither watercourses nor cliffs it was impossible to form any idea 

 of the geology, except of such rocks as cropped out at the surface. 



'N'othing more was to be seen of the flaggy sandstones and shales 

 of Cretaceous age, or of the conglomerates and marls noted at 

 Azimur. The whole country appeared to be covered to a consider- 

 able depth with a compact sheU-sand, full of fragments of Pecten 

 and Conus, all belonging, I judge, to Pliocene times. These deposits 

 are found at an ever-increasing elevation as one goes southward — 

 occurring as high as 700 feet above sea-level to the east of Saffi. 

 This is undoubtedly due to their inclusion within the area affected 

 by the upheaval of the Atlas — the district nearest the focus of 

 elevation having undergone the greatest upheaval. 



In travelling over these Tertiary lowlands it becomes very clear 

 to the explorer that the surface-features of the country are not such 

 as would result from subaerial denudation. On all sides, one sees 

 curious hummocky mounds and ridges with no determinate or general 

 trend, as well as cup-shaped and irregular hollows, which could 



1 [Maw, App. H to Hooker & Ball's ' Marocco & the Great Atlas ' (1878) 

 p. 453.] 



