but probably the siliceous schists, which are greatly developed in the upper divisions of the Mountain Limestone, represent the Culm or Millstone -grit. The position of the Russian-island limestone, which is widely spread, especially in Spitzbergen, is still doubtful ; for determinable fossils are wanting in it ; and the classification of the red shales in the Devonian is by no means certain. But although much still remains doubtful, we can see from clearly established facts that a remarkable and analogous development must have taken place in South Ireland and in Bear Island, high up in the north, and in the middle of Europe, in the formation of the rocks as well as in the plants and animals contained in them. Therefore the flora of the Ursa stage is of great significance in the history of the earth, as we shall see still more clearly if we cast a glance at the position which it holds in the order of the earth's development.
In the Silurian and Lower Devonian all the known plants and animals are marine ; and it is not until the Middle and Upper Devonian that land-plants, indicating dry land, make their appearance. Yet at present there are only a few localities known to us, which may be designated as Devonian islands : the neighbourhood of Saalfeld, in Thuringia, which belongs to the Upper Devonian, is the only one which has yielded a fairly respectable number of plants ; and even these have been found mostly in small fragments, which probably may have been divided into too many species. Towards the end of the Devonian period the dry land increases rapidly in the northern hemisphere ; it must have been a time of rising of the bed of the sea. With this great formation of dry land begins a new epoch — the Carboniferous. The first division of this I have called the Ursa stage. With it came in the first rich land-flora, which can be traced in the northern hemisphere, both of the Old and New World, from 47° to 74° and 76° K. lat. Everywhere it exhibits the same character ; everywhere appear Calamites radiatus (which probably clothed the marshy low country with its long column-like stems), the branching Lepidodendron, thickly clothed with leaves, and the curious Knorria. Even the Cyclostigmata, with which we have become acquainted in Ireland and Bear Island, were probably not wanting in dry-land formations lying between them, and formed part of the woods under whose shade the species of Cardiopteris and Paloeopteris spread out their powerful fronds.
This flora already comprises such a remarkable number of species, many of which appear in such widely distant regions, that it seems to indicate a wide-spread continent which was situated in the temperate as well as in the arctic zone. The coal-lands of Russia reached perhaps as far as Bear Island, the plants of which would then represent the most northern offshoots of the Russian Lower-Carboniferous flora. That the Ursa stage must have belonged to a land of considerable extent is shown by the freshwater animals found in it, the great pond-mussels (Anodonta) and the insects (all Neuroptera), They could only have lived in a land large enough to give rise to lakes and rivers.
It is difficult to decide how long this state of things lasted. Then
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