1872.] MAW PLAIN OF MOROCCO, 95 



beds, great masses of red porphyrites and tuffs are met with, asso- 

 ciated with specular iron and occasional green porphyries. The 

 harder portions of the latter are seen as Verde antique pebbles in the 

 river-beds ; but we failed to detect this in situ. Prom the large pro- 

 portion of tuffs that occurs the porphyrites appear to be interbedded, 

 and are possibly contemporaneous with the vertical grey shales to 

 which they are adjacent. They are overlapped unconformably by 

 the Red-Sandstone and Limestone series of Cretaceous age. Mr. 

 D. Forbes informs me that they bear a strong likeness to the por- 

 phyrites of the Andes, of Oolitic age ; but beyond the fact that they 

 were in existence and had undergone denudation into hill-and-val- 

 ley contour before the Cretaceous beds were deposited over them, 

 there is no certain evidence as to their age. 



There have been at least one or two subsequent intrusions of red 

 porphyrites, viz. of the dykes of Djeb Tezah, metamorphosing grey 

 shales into mica-schists, and of the dykes that break up through the 

 stratified beds of the plain east of Sheshawa — which are clearly 

 more recent than the porphyrites of the Atlas, as they penetrate 

 strata which extend over the denuded surface of the Atlas mass. 



(g) Eruptive Basalts. — Of these we met with three distinct species: 



(1) Black vesicular basalt (porous and compact pyroxenic lava 

 with olivine) on the coast near Mogador, and imbedded in the base 

 of the post-Tertiary concrete sandstone- cliffs: but it was nowhere seen 

 in situ ; and I think it possible that the fragments may have been 

 derived from the Canary Islands, which are only 70 or 80 miles 

 distant, or possibly from some point of eruption nearer the land. 



(2) Amygdaloid green Basalt, which rises up in dykes, in many 

 places penetrating the Red-Sandstone and Limestone series on the 

 flanks of the Atlas, and also piercing the diorite of the Arroond 

 valley. We observed numerous dykes at Tassemarout, Tassgirt, and 

 Asni, south-east and south of Morocco city. Beyond the fact that 

 they are probably post-Cretaceous, there is no evidence as to their 

 age. From what we could see of their distribution, the whole range 

 of the Atlas seems abundantly intersected by these dykes. 



(3) Diorite rises up in considerable masses among the porphyrites 

 in the valley of Arroond, due south of Morocco, but forms no great 

 proportion of the bulk of the ridge. Its intrusion may have been 

 contemporaneous with the dislocation and upturning of the Red- 

 Sandstone and Limestone series overlying the porphyries. 



General Summary. — It now only remains briefly to recapitulate 

 the order of sequence of the geological phenomena observed in the 

 plain of Morocco and the Atlas. 



The oldest rocks that have been noticed are : — 



(1) The ranges of rugged metamorphic rocks north of the city of 

 Morocco, and forming the northern boimdary of the plain, respecting 

 the age of which, and the period of their upheaval and metamorphism, 

 there is no evidence. 



(2) The interbedded porphyrites and porphyritic tuffs of the Atlas, 

 forming the backbone of the ridge, the age of which, and of the grey 

 shales with which they seem to be interbedded, is also uncertain. 



