THE GLACIAL PERIOD. 215 



In the Great Atlas terminal moraines 800 or 900 feet in 

 vertical height were observed by Sir Joseph Hooker, and Messrs. 

 Ball and Maw, 1 at an elevation of 6000 feet. They describe also 

 the occurrence of a remarkable series of ridges and rolling hum- 

 mocks and masses of angular debris, 300 or 400 feet in height, 

 and some 3000 feet above the sea-level, which extend along 

 the base of the great escarpment that rises abruptly from the 

 wide plains or table-lands of Marocco. The mounds do not rest 

 directly against the escarpment, but occur as " isolated mounds 

 200 or 300 feet in advance, sloping down towards the escarp- 

 ment in one direction, and in the other rolling away in great 

 wave-like ridges and undulating sheets, which terminate at a 

 well-marked line of demarcation, just where the level portion of 

 the plain commences." Where the internal structure of those 

 mounds was visible, the angular blocks of which they consisted 

 showed a disposition in layers sloping away from the escarp- 

 ment toward the plain. The stones had evidently been derived 

 from the lofty escarpment (1000 feet), and Mr. Maw thought 

 the mounds were "the result of glaciers covering the escarp- 

 ment, leaving on their recession the intermediate depression." 

 More recently M. Ch. Grad noticed what he took to be moraines 

 at the mouth of the gorge of El Kantara, on the southern side 

 of the Atlas in Algeria. These he describes as accumulations 

 of erratic debris, but he saw no polished rocks and no striated 

 stones. 2 I may note here in passing that Mr. Hartung observed 

 in the Azores a number of erratics of granite, which have evi- 

 dently been carried there by floating-ice. Even at the present 

 day icebergs go as far south as the latitude of those islands, but 

 they keep to the mid-ocean between the Azores and the Ameri- 

 can coast. When northern erratics were transported to the 

 Azores it is most probable that the Arctic Current extended 

 farther to east than it now does. 3 



1 Journal of a Tour in Marocco and the Great Atlas. See also Quart. Journ. 

 Geol. Soc, vol. xxviii. p. 85. 



2 Bull. Soc. G60I. France, 3 e Ser. t. i. p. 87. 



3 Origin of Species, 6th ed. p. *328. 



