stinguished from them with great difficulty. For example, the most abundant fern of St. John's, Pecopteris discrepans, Daws., is hardly to be distinguished from Pecopteris lonchitica, a species which, both in America and in Europe, is abundant in the Carboniferous. In the same manner, Cordaites Robbii, Daws., is so near C. borassifolius, Sternb., sp., that, according to Dawson, it may often be mistaken for it ; and Asterophyllites parvulus, Daws., is scarcely distinguishable from A. delicatulus, Sternb. (Bechera). Therefore the St.-John's flora has in fact the character of the Lower Carboniferous formation, and the only question is whether it does not approach more nearly to the Millstone- grit flora (with which it has five species in common) than to the Ursa stage. By this also it becomes doubtful whether the Catskill and Chemung groups do not belong rather to the Ursa stage than to the Upper Devonian.
In the arctic zone, besides the Bear-Island flora, we may regard the sandstones of Parry Island as belonging to the Ursa stage. In Melville Island also the sandstone lies under the Mountain Limestone; and the Knorria acicularis, which is found in it, serves as a point of contact with the Bear-Island flora, and shows that these plants of South Ireland and the Vosges reached as far as 76° N. lat.
If we add the plants of St. John, Kiltorkan, the Vosges, the south Black Forest, and the Verneuilii-shales to those of Bear Island, they yield to the Ursa stage a flora of seventy-seven known species, of which three are common to the Devonian and seven to the Middle Carboniferous. Of the former, however, one, and of the latter three species are doubtful, either in their determination or in their geological position. With the Upper Carboniferous (the Permian) the Ursa stage has not a single well-determined species in common ; with the Mountain Limestone it has thirteen species, and with the Millstone-grit twelve ; and with the two united, eighteen species. Among these are the most frequent species, such as form the true typical plants of the Lower Carboniferous, namely Calamites radiatus, Lepidodendron Veltheimianum, Knorria imbricata, Cardiopteris frondosa, and C. polymorpha. One of the most characteristic genera of the Ursa stage is Cyclostigma.
The flora of the Mountain Limestone and its equivalents appears to be less rich than that of the Ursa stage ; the culmiferous beds, on the contrary, have yielded a large number of plants, as have also the Greywacke and Posidonomya-shales of the Harz, Silesia, and Moravia. If we compare the plants from these different places, we find in each a number of peculiar forms, which probably arises from the flora being, as yet, so little known to us ; but we find also many species in common, which throughout are the most abundant and consequently the most important of the localities. These are chiefly the typical plants mentioned above. The Millstone-grit flora, when compared with that of tho Ursa stage, is remarkable for the increase in the number of species common to the Coal-measures ; among these are species which have a wide range through the formation, such as Neuropteris Loshii and Calamites Suckowii. The newer Greywacke, also, which forms a passage to the Coal-measures, is distinguished from them by the
vol,. XXVIII.— PART I. N
