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704 STRATIGRAPHICAL GEOLOGY. —[Boox VI. 
extent; for they are found turned up from under the newer formations 
along the flank of the Ural chain. It would thus seem that they spread 
continuously across the whole breadth of Russia in Europe. Though 
almost everywhere undisturbed, they afford evidence of some terrestrial 
oscillation between the time of their formation and that of the Silurian 
rocks on which they rest, for they are found gradually to overlap Upper 
and Lower Silurian beds. 
The chief interest of the Russian rocks of this age, as was first 
signalized by Murchison and his associates, lies in the union of the 
elsewhere distinct Devonian and Old Red Sandstone types. In some 
districts these rocks consist largely of limestones, in others of red 
sandstones and marls. Jn the former they present molluscs and other 
marine organisms of known Devonian species; in the latter they afford 
remains of fishes, some of which are specifically identical with those of 
the Old Red Sandstone of Scotland. The distribution of these two | 
paleontological facies in Russia is traced by Murchison to the litho- 
logical characters of the rocks, and consequent original diversities of 
physical conditions, rather than to differences of age. Indeed, cases 
occur where in the same band of rock Devonian shells and Old Red 
Sandstone fishes lie commingled. In the belt of the formation which 
extends southwards from Archangel and the White Sea, the strata 
consist of sands and marls, and contain only fish remains. ‘Traced 
through the Baltic provinces, they are found to pass into red and green 
marls, clays, thin limestones, and sandstones, with beds of gypsum. In 
some of the calcareous bands such fossils occur as Orthis striatula, 
Spiriferina prisca, Leptena productoides, Spirifera calcarata, Spirorbis ompha- 
loides, and Orthoceras subfusiforme. In the higher beds Holoptychius and 
other well-known fishes of the Upper Old Red Sandstone occur. Followed 
still further to the south, as far as the watershed between Orel and 
Woronesch, the Devonian rocks lose their red colour and sandy character, 
and become thin-bedded yellow limestones, and dolomites with soft 
green and blue marls. ‘Traces of salt deposits are indicated by occa- 
sional saline springs. It is evident that the geographical conditions 
of the Russian area during the Devonian period must have closely 
resembled those of the Rhine basin and central England during the 
Triassic period. 
The Russian Devonian rocks have been classified as follows : 
(Red and white sandstone and green marls,—numerous fish remains, 
Urrrer .{ particularly Holoptychius nobilissimus, Glyptosteus favosus, Dip- 
\ lopterus macrocephalus. 
(Limestones, clays, marls, dolomite, and gypsum,—numerous cha- 
Mipp.e.{ racteristic Devonian shells and crinoids, also Holoptychius 
\ nobilissimus. 
In some districts red and green limestones with red marls and 
Middle Devonian fossils; in others (North Livonia) sandstones 
Lower .4 and clays, with numerous fish remains of the genera Osteolepis, 
| Dipterus, Diplopterus, Asterolepis, and others found also in the 
| Caithness flags of Scotland, 
There is an unquestionable passage of the uppermost Devonian rocks 
of Russia into the base of the Carboniferous system. 
North America.—'T'he Devonian system, as developed in the 
northern States, and eastern Canada and Nova Scotia, presents much 
