FLORA. 205 
coal formation. We have designated under the name of 
Ursien stage the first sub-division of this period; with 
this coincides the appearance of the most ancient terres- 
trial vegetation sufficiently rich to give us an idea of the 
appearance presented by the vegetation at this primitive 
epoch, This flora was perhaps in fact spread across the 
northern hemisphere, both in the old and in the new 
continent from 47° to 74° or 75° of northern latitude; 
and everywhere it shows the same character. Everywhere 
appeared the calamites radiatus which covered with its 
high columnar stems the marshy lowlands, whilst it great 
rhizomes penetrated everywhere into the boggy soil. 
Everywhere also made themselves to be seen associated 
with them the wonderful Knorria, the Lepidodendron, 
with stems ramified dichotomously, and leaves united in a 
compressed plume. The Cyclostigma which we find both 
in the south of Jreland and in Bear Island, are also rarely 
awaunting in the bosom of the layers formed on an emerged 
soil; and these plants must have composed in} part the 
forests under the shade of which the Cardiopteris and 
Palaeopteris stretched their stout fronds. 
‘This flora comprised already a pretty considerable 
number of species ; and many of them showed themselves 
at the same time in regions so remote from one another, 
that their repeated presence warrants us to suspect the 
existence of a vast continent, stretching out both into the 
temperate and the arctic zone. The Russian carboniferous 
region prolonged itself probably to Bear Island; and the 
vegetation of this island would then have made an integral 
part of the lower carboniferous flora of Russia, of which it 
would mark the continuation towards the north—the proof 
that the Ursien stage must have been formed along the 
coasts of a great continent, resulting from the presence of 
fresh water animals, and pondal shells, and nervopters, 
which could not have lived but in a land sufficiently con- 
siderable to contain lakes and to give birth to-rivers. 
‘What was the duration of this period? That is a 
-point which one would fain determine! Then began a 
