The rest of the Daghestan region consists of a series of roughly parallel folds, of Jurassic or Cretaceous age, ranging in altitudes from 7500 up to 12,500 ft., separated from one another by deep gorge-like river glens which cut it up into a number of arid, treeless plateaus which have something of the appearance of independent ranges, or rather elongated tablelands of a mountainous character.
In most cases we have only the evidence of sterile fronds, and this is necessarily unsatisfactory; but the occurrence of numerous stems and fertile shoots demonstrates the wealth of Cycadean plants in many parts of the world, more particularly during the Jurassic and Wealden periods.
This genus has long been known as a common and widely spread Jurassic and Cretaceous conifer, but owing to the absence of petrified specimens and of well-preserved cones, it has been impossible to refer it to a definite position in the Coniferales.
The Klippen are isolated hills, chiefly of Jurassic limestone, rising up in the midst of the later and softer deposits on the inner border of the sandstone zone.
Seeds like those of Ginkgo biloba have also been recorded as fossils in Jurassic rocks, and it is possible that the type of flower known as Beania, from the Inferior Oolite rocks of Yorkshire, may have been borne by Ginkgo or Baiera.
Probably its original thickness Lough Neagh Tertiary Clays Eocene Basalt and Dolerite Cretaceous Trias, sometimes surmounted by Lower Jurassic Upper Carboniferous Carboniferous was not more than 150 ft., while now only from 40 to loo ft.
Coal occurs in many Jurassic fresh-water;basins, namely, on the outskirts of the Altai, in south Yeniseisk, about Irkutsk, in the Nerchinsk district, at many places in the Maritime province, and on the island of Sakhalin.
Cretaceous Jr. Jurassic Tr.
Reading flourishes from its position on the edge of the London Tertiary Basin, Croydon is a suburb of London, and Hull, though on the Chalk, derives its importance from the Humber estuary, which cuts through the Chalk and the Jurassic belts, to drain the Triassic plain and the Pennine region.
On the northern side granitic masses occur in the zone of Ariege amongst the Jurassic and Lower Cretaceous beds.