492 Dr. H. Trautschold—Periodical Movement of the Ocean. 
to the half of the Oolitic period, so beside the Stigmaria swamps 
and the above-mentioned fragments of wood in the Virgatus stratum 
of the Moscow Jura, there are also several other positive witnesses 
proving the existence of a continental epoch. One of these witnesses 
is a piece of Calamites arenaceus from the red sands of the river 
Wytchegda, another witness is a tooth of Ceratodus, found in a marl of 
Wetluga by M. Nikitin. Furthermore, M. Krotof has discovered on the 
Volga near Tumki, in the sandstone, fragments of the stems of Pinites 
biarmicus and freshwater shells like Unio umbonatus, Fisch., and U. 
castor, Kichw. Luckenberg has also found that the variegated marls, 
lying immediately under the Jurassic strata near Simbirsk, contain 
the same shells, together with Estheria minuta. Among the best 
witnesses of the continental period between the Carboniferous and 
the Jurassic periods are not only the rich flora of the copper sand- 
stone at the foot of the western Urals and the Steppe of Kargala, 
but also the gigantic Saurians and the fishes of the same sandstone, 
which enlivened the swamps and lakes and rivers of the Permian 
and Post-Permian period. And whilst this continental fauna and 
flora extended themselves over Russia, the shallow Permian sea con- 
tracted itself more and more, containing only a limited number of 
animals, which induced the French to give the name pénéen (zévys) 
to the Permian system, showing in the West of Europe the same 
poverty of species. A relative scarcity of species is also observable 
in the Russian Oolite, and this is not astonishing, if we take into 
consideration that owing to the shallowness of the narrow sea of that 
epoch a great number of pelagic animals must have been excluded. 
Towards the end of the Cretaceous period a second retreat of the 
sea from Huropean Russia took place. As the Russian sea of that 
time was in connexion with the ocean, the receding movement of the 
sea must have taken place as well to the north as to the south and 
west; it is therefore remarkable that in the northern part of Russia 
we find not a trace of Tertiary sediments. Are we entitled to think 
that the Russian sea at the Tertiary period was depressed only to 
the south?! But if that was the case, nevertheless, the whole 
ocean participated in the movement, and the Tertiary sea must have 
left its shells on the shores of Arctic Russia as well as the post- 
Tertiary ocean left its shells during its gradual retreat at the mouth 
of the valleys of the Dwina and Petchora. Moreover, during the 
Tertiary period there was no mountan chain that could prevent the 
flowing off of the sea-water. 
It is remarkable also that the northern half of Russia, after having 
become for the second time a continent, only became habitable for 
lower and higher animals very late. I have already mentioned in 
my former papers that its eluvium and alluvium do not contain even 
traces of shells, and that the upper layers of dry land formation 
contain only remains of Mammoth, Rhinoceros tichorhinus, Bos 
priscus, Cervus megaceros, etc. . Evidently during the whole Tertiary 
1 We find here in regular succession the Tertiary sediments one after the other, 
the older occupying the higher points of the plain, the younger the lowest near the 
shores of the Caspian and Black Sea, and between these basins. 
