Arkell.1956.Jurassic..

626 GENERAL SURVEY
and of mountain-building in the Caledonian and Variscan orogenies were
in part above water in the Jurassic and formed extensions of the shields
(e.g. Ural Mountains, Kuen Lun), but in part were submerged and formed
labile shelves, on which varied Jurassics were formed in troughs, often
interspersed with horsts (e.g. extra-Alpine Europe).
The mobile belts so conspicuous at the present day are a heritage from
the Tertiary orogeny and do not coincide entirely with any easily recognized
combination of features in the Jurassic. The circum-Pacific mobile
belt was the most actively mobile in Jurassic times and provides the
TABLE 25.—CERTAIN FEATURES OF THE JURASSIC SYSTEM AS DEVELOPED
IN SOME OF THE CHIEF TERTIARY MOUNTAIN RANGES
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Mountain ranges in the
Tertiary mobile belt
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V U H H Q > Plutoni;
+ + + 4-
+
Rockies + +
Andes . . . . + + + +
New Zealand + + + +
+
[Eastern Australia] . +
+
Canadian coast ranges +
Californian coast ranges .
+ + + 4- -J-
Himalayas
Elburz .
Caucasus
Crimea
Atlas .
Alps .
.
.
.
.
.
.
.
.
.
+
+
+
+
+ +
-F 4-
+ + + +
Pyrenees +
greatest number of special characters. In North America it was the
scene of active volcanism, geosynclinal subsidence and sedimentation,
orogeny and batholith intrusion, all in Jurassic times. The Tertiary
mobile belt, however, takes in the Rocky Mountains, which was a nonvolcanic,
non-orogenic, shelf-sea during the Jurassic. In eastern Australia
the analogue was not incorporated in the Tertiary mobile belt, which
coincided with the Jurassic geosyncline (New Guinea—New Caledonia—
New Zealand). This geosyncline qualifies as such and as a mobile belt
by its great thickness of Jurassic greywacke and flysch-type sediments
(approaching 5000 m.) and conglomerates, but it shows only feeble Jurassic
volcanism, no plutonism and no folding.
The east-west mobile belt across southern Asia and Europe coincides
approximately with the Tethys sea of the Jurassic. On the whole it was
mainly a mobile belt in the Jurassic, but it embraced within it many areas
of stable shelf and rising horsts, and many of its mobile parts would, by
themselves, be classed only as labile shelves. The Himalayas do not
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