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Updated: June 10, 2025
The sheet of water, lying at a tolerably great depth underground, but already sounded by two bores, is furnished by the layer of green clay situated between the chalk and the Jurassic lime-stone; this layer may be represented by a disk five and twenty leagues in circumference; a multitude of rivers and brooks ooze there; one drinks the Seine, the Marne, the Yonne, the Oise, the Aisne, the Cher, the Vienne and the Loire in a glass of water from the well of Grenelle.
The tract of which this celebrated district forms a part lies as it were in a bay of the Apennine limestone of Jurassic age. The floor of this bay is composed of puzzolana, a name given to beds of volcanic tuff of great thickness, and rising into considerable hills in the vicinity of the city of Naples, such as that of St. Elmo.
Flying reptiles also evolved, to set an example for the bats of the mammalian class, for both kinds of flying organisms converted their anterior limbs into wings, although in different ways. During the Triassic and Jurassic periods of the Mesozoic age, the first birds and mammals appeared to follow out their diverging and independent lines of descent.
On either side the cliffs rose higher, and the walls of Jurassic rock, above the brashy steeps, more towering, precipitous, and fantastic. Where vegetable life could draw sustenance from crumbling, stones stretched a veritable forest of box. Now, in a narrow gorge, the Dourbie frolicked about the heaps of pebbles it had thrown up in its winter fury.
Nevertheless, we can only go upon the facts before us; and if we compare our existing fauna with the fauna of Jurassic and Pliocene times, we shall at any rate be putting it to the test of the severest competition that lies within our power under the actual circumstances. In the Jurassic age there were undoubtedly a great many very big reptiles.
Their gait is slow and deliberate, but so enormous are their strides that, as a matter of fact, they cover the ground quite rapidly. Perry has told me that they are almost identical with the fossilized remains of the diplodocus of the outer crust's Jurassic age. I have to take his word for it and I guess you will, unless you know more of such matters than I.
Blake has made fine colored drawings of it, which may be published at some future time. . .The family of the Pleurotomariae numbers between four and five hundred fossil species, beginning in the Silurian deposits, but especially numerous in the carboniferous and jurassic formations. The sponges afford another interesting case.
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.
Now, the fact as to the comparative size of our own cetaceans and of 'geological' animals is just this. The Atlantosaurus of the Western American Jurassic beds, a great erect lizard, is the very largest creature ever known to have inhabited this sublunary sphere.
Of about 180,000 species of plants in nature to-day more than 100,000 are Angiosperms; yet up to the end of the Jurassic not a single true Angiosperm is found in the geological record. This is a broad manifestation of evolution, but it is not quite an accurate statement, and its inexactness still more strongly confirms the theory of evolution.
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