Arkell.1956.Jurassic..

BORDERS OF THE MASSIF CENTRAL 6 9
EASTERN AND SOUTHERN BORDERS OF THE MASSIF CENTRAL
The Massif Central is bounded on the east by the broad alluvial valley
of the Rhone and Saone, which is a tectonic depression comparable to
the middle Rhine. The faulting has carried the Jurassic rocks down
below the alluvium and Tertiaries, and between Lyon and Valence the
FIG. 6.—Map of the Jurassic outcrops in the south-east of France.
ancient rocks of the massif abut against the river. North and south,
however, a narrow and discontinuous fringe of Mesozoics remains west
of the river. This fringe is important out of all proportion to its small
area of outcrop. In it the Lias and Tithonian take on their Mediterranean
facies. Just as from the north the Jurassic of the Paris Basin spreads
through the Langres portal and fringes the massif through the Cote
d'Or and Maconnais, with an outpost in the Mont d'Or, NW. of Lyon,
so in the south the Jurassic deposits swing round the southern border
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