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On the whole, the organic remains and the geological position of the strata prove distinctly that in the neighbourhood of Aix-la-Chapelle a gulf of the ancient Cretaceous sea was bounded by land composed of Devonian rocks.
This led to a more thorough investigation of the different sets of strata, resulting in the establishment by D'Orbigny of a still greater number of periods, marked by the successive deposits of the Jurassic and Cretaceous seas, all of which contained different organic remains.
His wife span and he delved; he dug the clay, and she formed it with her fingers into vessels, on which to this day her finger-prints may be found. These caves are hollowed out in a thick bed of cretaceous rock. The habitations are divided into two unequal parts by a wall cut in the living chalk.
Again, as during the Triassic, a warping of the crust formed a long trough parallel to the coast and to the Appalachian ridges, but cut off from the sea; and here the continental deposits of the early Cretaceous were laid.
I need not continue the enumeration. Suffice it to say that the facts justify the conclusion which Lesquereux a scrupulous investigator has already announced: that "the essential types of our actual flora are marked in the Cretaceous period, and have come to us after passing, without notable changes, through the Tertiary formations of our continent."
To return to an example already given: All competent authorities will probably assent to the proposition that physical geology does not enable us in any way to reply to this question Were the British Cretaceous rocks deposited at the same time as those of India, or are they a million of years younger or a million of years older? Is palaeontology able to succeed where physical geology fails?
It is therefore clear that the elevatory forces which gave rise to the mountains operated subsequently to the Cretaceous epoch; and that the mountains themselves are largely made up of the materials deposited in the sea which once occupied their place.
All this is certain, because rocks of cretaceous or still later date have shared in the elevatory movements which gave rise to these mountain chains; and may be found perched up, in some cases, many thousand feet high upon their flanks.
Between the Alleghany Mountains, formed of older rocks, and the Atlantic, there intervenes, in the United States, a low region occupied principally by beds of marl, clay, and sand, consisting of the cretaceous and tertiary formations, and chiefly of the latter. The general elevation of this plain bordering the Atlantic does not exceed 100 feet, although it is sometimes several hundred feet high.
No feathered creatures so closely approach the lizard-tailed birds of the oolite or the toothed birds of the cretaceous period as do these Australian and New Zealand emus and apteryxes.
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