GEOLOGY OF MAROCCO AND GREAT ATLAS. 465 



fact that they were in existence and had undergone denuda- 

 tion into hill-and-valley contour before the Cretaceous beds 

 were deposited over them, there is no certain evidence as to 

 their age. 



There may have been at least one or two subsequent intru- 

 sions of red porphyrites, viz. of the dykes of Djebel Tezah, 

 metamorphosing grey shales into mica-schists, and of the dykes 

 that break up through the stratified beds of the plain east of 

 Sheshaoua — which may probably be more recent than the por- 

 phyrites of the Atlas, as they appear to penetrate strata which 

 extend over the denuded surface of the Atlas mass ; but I can- 

 not speak with certainty as to the relative age of the stratified 

 beds and the porphyritic bosses which rise up out of the plain. 



(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 Arround valley. We observed numerous dykes at Tasse- 

 remout, Tassgirt, and Asni, south-east and south of Marocoo 

 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 por- 

 phyrites in the valley of the Arround, due south of Marocco, 

 but forms no great proportion of the bulk of the ridge. Its in- 

 trusion may have been contemporaneous with the dislocation 

 and upturning of the Red Sandstone and Limestone series over- 

 lying the porphyrites. 



General Summary. — It now only remains briefly to reca- 

 pitulate the order of sequence of the geological phenomena 

 observed in the plain of Marocco and the Atlas. 



