Geological Society of London. 135 



that represented as G. minutum. He considered that the four supposed species 

 belonging to three genera were only different forms of the same plant. 



2. " Notes on the Geology of the Plain of Marocco, and the Great 

 Atlas." By George Maw, Esq., F.G.S. etc. 



The author described first the characters presented by the coast of 

 Marocco, and then the phenomena observed by him in his progress 

 into the interior of the country and in the Atlas Chain. The oldest 

 rocks observed were ranges of metamorphic rocks bounding the 

 plain of Marocco, interbedded porphyrites and the porphyritic tuffs 

 forming the backbone of the Atlas Chain, and the Mica-schists of 

 Djeb Tezah in the Atlas. At many points in the lateral valleys of 

 the Atlas almost vertical grey shales were crossed ; the age of these 

 was unknown. Above these comes a Eed Sandstone and Limestone 

 series, believed to be of Cretaceous age, and beds possibly of 

 Miocene age, which occupied the valleys of the Atlas and covered the 

 plain of Marocco, where vestiges of them remain in the form of 

 tabular hills. The probable age of these beds was determined on 

 the evidence of fossils. The author noticed the sequence of de- 

 nuding and eruptive phenomena by which the arrangement and 

 distribution of these rocks has been modified, and described the 

 more recent changes resulting in the formation of enormous boulder- 

 beds flanking the northern escarpment of the Atlas plateau, and of 

 great moraines at the heads of the valleys of the Atlas, both of which 

 he ascribed to glacial action. An elevation of the coast line of at 

 least 70 feet was indicated by raised beaches of concrete sand at 

 Mogador and elsewhere, and the author considered that a slight sub- 

 sidence of the coast was now taking place. The surface of the plain 

 of Marocco was described as covered with a tufaceous crust, probably 

 due to the drawing up of water to the surface from the subjacent 

 calcareous strata and the deposition from it of laminated carbonate 

 of lime. 



Discussion. — Mr. Ball, as an Alpine traveller who had also visited the Atlas in 

 company with Dr. Hooker and Mr. Maw, offered a few remarks. The plane of 

 Marocco was not, in his opinion, a level, but an inclined plane, rising gradually in 

 height up to the foot of the mountain, so that the base of the boulder ridges was at 

 some height above the level of the plain near Marocco. He did not think that the 

 boulder deposits could be safely attributed to glaciers, but thought rather that they 

 had been carried into and deposited in a shallow sea. He thought also that Mr. Maw 

 had somewhat over-estimated the thickness of some of the boulder deposits ; and 

 though there was one instance of an undoubted moraine in one of the higher valleys 

 of the Atlas, yet he could not agree in the view that the glaciation of the Atlas was 

 general. He could not accept such a great thickness of beds as that represented by 

 the vertical shales in Mr. Maw's section. 



Prof. Eamsay was pleased that the author, though giving so many interesting de- 

 tails, had not assigned any definite age to many of the beds. He agreed with him as 

 to the cause assigned for the great tufaceous coating of the country. He had already 

 assigned the same cause for the existence of certain saline beds, and would attribute 

 the existence of the great coating of gypsum at a slight depth below the surface of 

 the Sahara to the same cause. As to the existence of moraines, he was not surprised 

 to find them in the Atlas, as they were already known in the mountains of Granada. 

 As to the escarpments, it was now well known that, as a rule, they assumed a direc- 

 tion approximately at right angles to the dip of the strata ; and he felt inclined to 

 consider that the bulk of the mounds at the foot of the escarpment of the Atlas were 

 rather the remains of a long series of landslips from the face of the cliffs than to an 

 accumulation of moraine matter. 



