116 Geological Society. 



2. ' The Greology of Southern Morocco and the Atlas Mountains.' 

 By the late Joseph Thomson, Esq. 



This paper gives the results of observations made under con- 

 siderable difficulties during a journey in Morocco in 1888. The 

 tract traversed is roughly triangular, the base being the Atlantic 

 Ocean between Saffi and Agadir, and the apex the district of Deninat 

 on the northern slopes of the Atlas, some 60 miles east of the city 

 of Morocco. This district consists of three main sections : — (1) The 

 Coast Lowlands ; (2) the Plateau in two chief steps, the northern 

 rising to 2000 and the southern to 5000 feet ; (3) the Atlas itself, 

 which only begins to be a mountain-chain about 30 miles from the 

 coast, and which ranges first east-by-north and then north-east in 

 its central and loftiest part. 



(1) The Low r lands are practically conterminous with the Tertiary 

 deposits, among w 7 hich apparently Eocene, Miocene, and Pliocene 

 rocks are represented. The latter consist of shelly sands 200 to 

 300 feet thick, gradually rising to a height of 700 feet south 

 and east of SafH. Their surface is often covered with the slaggy 

 tufaceous crust described by Maw. The local presence of this 

 crust and the porous character of the deposit elsewhere have pre- 

 served it from denudation, and thus (in the opinion of the author) 

 its surface still presents the appearance of the Tertiary sea-bed on 

 which it was formed. Certain quarry-like pits, one of which 

 contains a pillar of wbite crystalline calcium carbonate, are sup- 

 posed to be due to the explosion of steam connected with the 

 existence of hot springs. 



(2) The Plateau is underlain by three rock- formations : — 

 (a) Metamorphic rocks including clay-slates, which probably under 

 lie the whole Plain of Morocco and rise into a group of rugged hills 

 called the ' Jebelet,' in contradistinction to the ' Jebel ' or Atlas 

 proper. (6) The Lower Cretaceous rocks, consisting of red shales and 

 sandstones, the former frequently giving rise to brine springs and 

 containing salt-deposits at .Demnat in the Atlas, (c) The Upper 

 Cretaceous rocks, chiefly white and cream-coloured limestones, which 

 attain their greatest development on the Plateau. 



(3) The Atlas itself is made up for the most part of the same 

 rocks. There is a core of metamorphic rocks, which is better 

 developed and wider at the western end of the range and narrower 

 towards the east. Next comes the great development of the Lower 

 Cretaceous strata, followed by a diminutive representative of the 

 Upper Cretaceous rocks. These rocks are much broken by folding 

 and faulting, and their structure is displayed in several sections 

 taken across the range from Demnat westward. The first signs of 

 glacial action were met with at Titula, consisting of moraine-like 

 heaps of debris ; elsewhere, scratched stones w 7 ere found. The 

 Boulder-deposits described by Maw were not seen either east or 

 west of the locality described by that author ; but Maw's original 

 section was not traversed, and the present author does not offer any 

 opinion as to the origin of the beds. Intrusive basalts penetrate the 

 Cretaceous rocks, while porphyrites, diorites, and other igneous rocks 

 pierce the metamorphic rocks of the central core. 



