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Updated: June 10, 2025
Davidson on the British Brachiopoda, illustrates, in the first place, the tendency of certain generic forms in this division of the mollusca to be persistent throughout the whole range of geological time yet known to us; for the four genera, Rhynchonella, Crania, Discina, and Lingula, have been traced through the Silurian, Devonian, Carboniferous, Permian, Jurassic, Cretaceous, Tertiary, and Recent periods, and still retain in the existing seas the identical shape and character which they exhibited in the earliest formations.
The remains of reefs formed by coral polypes of different kinds from those which exist now, enter largely into the composition of the limestones of the Jurassic period; and still more widely different coral polypes have contributed their quota to the vast thickness of the carboniferous and Devonian strata.
Viewed as reptiles, we have certainly nothing at all to come up to these; but our cetaceans, as a group, show an assemblage of species which could very favourably compete with the whole lot of Jurassic saurians at any cattle show. Indeed, if it came to tonnage, I believe a good blubbery right-whale could easily give points to any deinosaur that ever moved upon oolitic continents.
In this new structure they would have no preponderant advantage as long as the genial Jurassic age favoured the great reptiles, and they may have remained as small and insignificant as the Marsupials.
These sea monsters disported along the Pacific shore over northern California in Triassic times, and the bones of immense members of the family occur in the Jurassic strata of Wyoming. Like whales and seals, the ichthyosaurs were descended from land vertebrates which had become adapted to a marine habitat. PLESIOSAURS were another order which ranged throughout the Mesozoic.
"Here," said he, pointing to the picture of an extraordinary flying monster, "is an excellent reproduction of the dimorphodon, or pterodactyl, a flying reptile of the Jurassic period. On the next page is a diagram of the mechanism of its wing. Kindly compare it with the specimen in your hand." A wave of amazement passed over me as I looked. I was convinced. There could be no getting away from it.
The foundation rock is sometimes metamorphic schist, or gneiss, at other times sandstone referred by Hislop to Jurassic age; and in no single instance has a volcanic crater or focus of eruption been observed. But outside the central trappean area volcanic foci are numerous, as in Cutch, the Rajhipla Hills and the Lower Narbudda valley.
This tract was separated from that of the Neapolitan volcanic region by a range of limestone hills of Jurassic age between Segni and Gaeta, a protrusion of the Alban Hills westward; but the general structure and physical history of both regions are probably very similar, with the exception that the igneous forces still retain their vitality in the more southerly region.
This terre bleue, as the peasants call it, was not the only sign of a change in the formation; fragments of calcareous stone were mixed with the brown soil. I was leaving the dark schist and was approaching those immense accumulations of jurassic rock, whose singular forms and brilliant colours lend such extraordinary grandeur to the scenery of the Upper Tarn.
There are important coal-beds in India of Permian age. There are coal-beds of Liassic age in South Hungary and in Texas, and of Jurassic age in Virginia, as well as at Brora in Sutherlandshire; there are coals of Cretaceous age in Moravia, and valuable Miocene Tertiary coals in Hungary and the Austrian Alps. Again, older than the true carboniferous age, are the Silurian anthracites of Co.
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