1920.] of the Mar ocean "Middle- Atlas.'' 267 



own, clearly separated from its sister by the ever-widening 

 valley of the 0. IvPlouya. The final 60 miles of the chain is 

 spread out in a (quadrangular mountain expanse of some 

 1500 square mileSj one main line of peaks running N.4:0°E. 

 to form the eastern terminus ; another, containing the 

 dominant massif of Moussa on Saleh (12,425 feet), curves 

 gradually to the northward, and forms the northern terminus 

 of the chain near Taza. 



It is thought that, as in the case of the Great-Atlas, the 

 first upheavals of the ]\[iddle-Atlas occurred during late 

 Primary and early Secondary times, and that later, the basal 

 plateaux of Jurassic formation emerged from the sea^ placing 

 above water the whole range with ils present trend as we 

 now know it. 



Elevation over perhaps all Marocco continued, and there 

 is good evidence to show that in Miocene times, all the 

 Hanking hills and plateaux (including the plateaux of 

 El Hajeb and Oulmes) to the northward of the Middle-Atlas 

 were also above water, their bases washed by a sea that 

 connected the Mediterranean and Atlantic — and separated 

 from Africa the RifF chain, at a time when the latter was 

 joined to Europe. 



The theory is, briefly, that the Uiff belongs fundamentally 

 to the Andalusian Sierra Nevada, that up to (probably) 

 Pliocene times the two were connected by dry land via 

 Apes Hill — Gibraltar, in the West ; and in the East (doubt- 

 fully ever above water) via Blelilla — Alboran Island — (Ja})e 

 de Gata ; and that the Mediterrano-Atlantic connection, 

 admitted as having existed at this period, was by the 

 " detroit Sud-Rifain "' of French geologists, which, it may 

 be noted, equally cut off both the Algerian Tell and 

 Middle-Atlas from the Riff. 



This phase had been preceded by one in which the Sierra 

 Nevada was itself isolated from Europe by the " detroit nord 

 Boetique," and was succeeded by that which simultaneously 

 (in geologic chronology) closed the ".detroit sud-Rifain '" 

 and opened the Straits of Gil)raltar, so as to group the land 

 and sea areas as thev exist to-dav. 



