There may have been at least one or two subsequent intrusions 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 porphyrites of the Atlas, as they appear to penetrate strata which extend over the denuded surface of the Atlas mass; but I cannot 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 Tasseremout, Tassgirt, and Asni, south-east and south of Marocco 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 the Arround, due south of Marocco, 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 porphyrites.
General Summary.—It now only remains briefly to recapitulate the order of sequence of the geological phenomena observed in the plain of Marocco and the Atlas.
The oldest rocks that have been noticed are:—
(1) The ranges of rugged metamorphic rocks north of the city of Marocco, and forming the northern boundary 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.
(3) Mica-schists of Djebel Tezah, in the Atlas, south-west of Marocco, pierced with eruptive porphyritic dykes, which may be an altered condition of the vertical grey shales adjacent to the interbedded porphyrites.