Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/73

1868.] MURCHISON—north-western Siberia. 3 condensing, to form a bar to to all future outburst, and thus save these vast regions from the earthquakes, dislocations, and ruin which have for ages affected all those countries wherein the issue of such internal forces is not checked, and particularly where great fissures or deep longitudinal cracks in the crust exist.

The Ural Mountains, lying as they do between two vast undisturbed regions, and replete as they are with many varieties of such eruptive rocks, afford a fine illustration of this view.

So also at several points around the centre of Russia in Europe, as in the environs of Petrozavodsk and the Lake Onega in the north, and in the region of the Southern Steppes.

It is within these zones of subterranean disturbance that the huge and wide-spread deposits of Russia and Siberia exhibit unquestionable proofs that they have been disturbed violently. They have simply undergone equable movements of elevation and depression, and exhibit strata of very high antiquity, often covered with Postpliocene and arctic deposits, which, if we judged merely from the conformity of their mutual arrangement, might be supposed to be of the same or nearly the same age, though in reality they were separated by long epochs in time.

In regard to the geology of Russia in Europe, Count Keyserling informs me that M. Grewinck has discovered white fossiliferous chalk in parts of the great Sarmatian plain, where its existence was unknown owing to the cover of Quaternary and allied deposits:—

1. At Baltishke, north-east of Kovno, and near the banks of the river Noveja, where the rock is covered by 4 or 5 feet of Quaternary deposit, it contains the following fossils—Rotulina trachyomphala (Reuss), Cristellaria rotulata (Lam.), Rotulina polyraphis (Reuss), Fromentulina levigata (Romer), Bulimina intermedia (Reuss), Textillaria globifera (Reuss), Globigerina cretacea (D'Orb.), Frondularia Dentalina, Cytherea, of species not determined, with species of Echinoderms and large Inocerami. 2. At Melden, a country-house in Courland, on the river Lendisk, below Nigrande, where, beneath a cover of lignite, beds of chalk with several of the above-mentioned fossils, including Inocerami, repose on Permian rocks.

These Cretaceous rocks, separated by great distances, seem closely to resemble those of Lemberg in Gallicia, and of Grodno in Russia; so that we may infer that, originally, the chalk formation had a very wide extension in this region, whilst we know that it appears in force low down the Volga and in the Government of Orenburg. Its denudation in the two localities cited accounts for the great admixture of chalk flint which is found in the so-called drift of these tracts.

M. Grewinck has also made inquiries into the real source of the vast quantities of amber which are found on the beach or by dredge along the shore near Memel*. He suggests that it may be carried down by rivers into that sea from the deposits of that age which occupy the large adjacent region of Russia and Poland. I am the more disposed to believe that these interior tracts are truly those


 * [On this point see Dr. Zaddach's memoir on Amber, translated in 'Quarterly Journal of Science' for April.—H. M. J.]

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