Arkell.1956.Jurassic..

258 NORTH AFRICA
and although movements occurred along it again in post-Miocene and
even (at least locally at either end) in post-Pliocene times (Laffitte, 1939).
Owing to a regional tilt or pitch of the whole of Barbary and the adjoining
Sahara plateau towards the east, Jurassic outcrops are much more extensive
in Morocco and diminish progressively through Algeria, until in
Tunisia they consist of only scattered inliers in the crests of anticlines,
separated by broad stretches of Cretaceous and Tertiary rocks. To some
extent this distribution is due to tilting during the Jurassic, for there is
reason to believe that in much of Morocco, in the Middle Atlas region
especially, deposition ceased with the Bathonian and no Upper Jurassic
ever existed.
The Tertiary folding of Barbary took place at two main periods. There
was an extensive Upper Eocene-Lower Oligocene (Pyrenean) phase
which has left a predominantly SW.-NE. grain in the High Atlas, Saharan
Atlas and Middle Atlas of the south and west, and in the north and east
Neogene folding superimposed a predominantly W.-E. grain in the
Mediterranean or Tellian Atlas. The reticulate pattern resulting from
the two phases of folding, and many local complications (in part due to
movements of Triassic salt), have made the geological map of Barbary
very complex. In general, however, the folding is simple, consisting of
narrow anticlines and periclines, sometimes accompanied by overfolding
and local thrusting, separated by relatively broad level tracts. Between
the High and Saharan Atlas in the south and the Tellian Atlas in the
north is a stable area occupied by the Plateau of the Shotts and high
limestone 'causses'. These areas were almost unaffected by Tertiary
folding, except along oblique SW.-NE. lines of the Middle Atlas, and they
have been compared to the similar mesetas of Spain.
Thus, with one exception, all the mountains of Barbary belong to the
southern autochthonous fold zone of the Alpine orogen.
The exception is the Rif of Morocco, an arcuate belt of major thrusts
which continues the Betic Cordillera of Spain in the form of a horseshoe.
A masterly monograph by Fallot (1937) shows the main range to consist
of autochthonous Triassic dolomites, more than 1000 m. thick and overlain
by Lias, thrust outwards (i.e. to the SW.) over Cretaceous and Eocene
flysch in a series of small nappes, and in turn overthrust in the same
direction by Palaeozoics. This is evidently a fragment of the inner or
thrust zone of the orogen. Other fragments may be recognized in the
Kabylie and its continuation on the coast each side of Algiers. To account
for the horseshoe shape of the Betic-Rif thrust arc it seems necessary to
postulate a median mass foundered under the western Mediterranean.
The movements occurred mainly in the Neogene (Fallot, 1941).
Within the autochthonous folded zone that comprises most of Barbary
the Jurassic stratigraphy is by no means simple or straightforward.
There are complex changes of facies, both horizontal and vertical, great
variations of thickness, and disconformities, which indicate minor folding,
faulting and horst-formation within Jurassic times: movements that
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