AGE OF THE ATLAS MOUNTAINS. 247 



the sea. In it there are rocks of the primitive class, as 

 granite, gneiss, mica-slate, and clay-slate. Copper and 

 lead mines, said to occur in the primitive parts of the range, 

 were worked by the ancients in Morocco and Algiers, but 

 are at present neglected ; and the same is also the case 

 with the antimony and tin (l) said to have been discovered 

 in these mountains. In Tunis, rock-crystals, graphite, or 

 black-lead, and also iron and galena, are met with in the 

 same kinds of rock. Although in extensive mountain- 

 ranges the older rocks, or those of the primitive class, gene- 

 rally predominate, such, according to travellers, is not the 

 case with the Atlas, where the most extensive deposites are 

 of a calcareous nature. This calcareous formation consists 

 principally of secondary limestones, associated with depo- 

 sites of sandstone. The limestone abounds with organic 

 remains, as of shells, corals, and even fishes ; and is said 

 to be referable to the various limestones extending from 

 the lias, or even the magnesian limestone, to chalk inclu- 

 sive. Hence in this limestone-range there are magnesian 

 limestones, oolite limestones, lias limestones, Jura lime- 

 stones, and soft limestones resembling some kinds of chalk. 

 Resting upon these limestones, or where they are wanting, 

 as is the case at Algiers, there are deposites of tertiary 

 rocks ; these are marly clays and limestones, with organic 

 remains resembling those met with in the tertiary deposites 

 on the north shore of the Mediterranean. Salt springs and 

 gypsum are mentioned as occurring in different parts of the 

 range. These may be connected either with the secondary 

 or tertiary, or with both classes of rocks. 



Trap-rocks, of a modem date, also make their appearance 

 among the rocks of the northern African zone. The most 

 extensive display of these Plutonian masses is in the lime- 

 stone in some districts to the south of Tripoli, where these 

 rocks alter the position and change the characters of the 

 limestone. 



Age of the Atlas Mountains. — It is conjectured, by some 

 geologists, that the great ranges of mountains of the earth 

 have risen from below, through rents in previously existing 

 strata, and not all at once, but at different times ; and fur- 

 ther, that all mountain ranges having the same general 

 direction have made their appearance from below at the 



