An attempt has been made to prove that an upland vegetation of very different character existed contemporaneously with it, but reasons will be given in the sequel for concluding that this supposed upland Carboniferous flora is everywhere of later date.
The later shallow-water phase of Carboniferous times, as already stated, was unusually long, it was also very widespread, and appears to have been accompanied over wide areas by humid conditions during its continuance, and accordingly the marsh conditions which existed during Upper Carboniferous times were probably on a larger scale than that of similar conditions before or after. Special stress is laid upon this fact, as it is a good illustration of the view which seems to be gaining ground, that every period possessed peculiar conditions never to be repeated, which must have left their impress upon the character of the sediments.
Though the conditions above described were widespread, they were naturally not universal, and accordingly in many parts of the world, as previously stated, we find true marine deposits of Upper Carboniferous times, though even these were sometimes replaced during part of the epoch, by conditions which were favourable for the formation of coal-seams in those places. Interruption in the continuance of a humid temperate climate over the regions of North-West Europe is also suggested by the discovery of deposits which are maintained to be of glacial origin amongst the Coal Measures of France[90].
[90] For an account of the numerous volcanic products see Sir A. Geikie's work on "The Ancient Volcanoes of Great Britain."
The Floras and Faunas. The flora of the Carboniferous rock is so noteworthy that the period has been termed the Period of Cryptogams; the remains of ferns, horsetails, and clubmosses predominate, and many of the forms reached a gigantic size. Though the floras of the various stages are marked by a general resemblance, there are differences which enable the palæobotanist to ascertain the stratigraphical position of the beds by reference to the included plant remains, and a considerable number of successive floras have been described[91]. The invertebrate fauna does not differ on the whole very greatly from that of Devonian times, though the trilobites are now becoming rare, and the mollusca assume a more prominent position as compared with the brachiopods. Corals occur in abundance in the calcareous deposits of the period, and frequently give rise to sheets of reef-formation, but the foraminifera and crinoidea certainly play the principal part as limestone-producers, and the influence of the latter in giving rise to great masses of limestone which are frequently used for ornamental purposes is too well known to need more than passing reference. The air-breathers have also been detected in greater abundance, though they are rare, when we consider the comparatively favourable conditions for their preservation presented by the Coal Measure rocks. Myriopods, arachnids, insects and pulmoniferous gastropods have however been found with tolerable frequency. The danger of arguing from imperfect data is well illustrated by the great addition to our knowledge of the insect-fauna of these times due to the exploration of the beds of one small coal-field, that of Commentry in France, of which the insects have been described by M. C. Brongniart. The vertebrates are represented by a considerable variety of fishes, and less abundant though tolerably numerous remains of Amphibia, which occur in the Carboniferous rocks of the North of England, Ireland, France, North America and elsewhere.
[91] Consult Kidston, R., "On the Various Divisions of the Carboniferous Rocks as determined by their Fossil Flora," Proc. Roy. Phys. Soc. Edin., vol. XII. p. 183.
The existence of definite zones of organisms in the case of the Carboniferous rocks has been denied, and it appears to be considered by some that the Carboniferous rocks were accumulated so rapidly as compared with rocks of some other systems that the fauna remained very similar throughout. It is very doubtful if this was so. In the case of other systems, the division into zones has only been accomplished by means of more detailed researches than those which have been conducted amongst the Carboniferous rocks of Britain: again, the occurrence of successive floras suggests that there may have been a similar succession amongst the faunas, and finally we find that zonal division has been carried on to some extent amongst the Carboniferous strata of other regions. The following classification of the Russian type of sediment may prove useful, as an indication of the possibility of more detailed separation of our own beds:—
| Gshellian (with Fusulina and Archimedipora) | Beds with Spirifera fascigera, Spiriferina Saranae, &c. Beds with Producta cora, P. uralica, Camarophoria crumena, &c. Beds with Syringopora parallela and Spirifera striata. | |
| Moscovian | Stage of Spirifera mosquensis. | |
| Lower Carboniferous | Stage of Spirifera Kleini. Coals, Sandstones and Shales with Noeggerathia tenuistriata and Producta gigantea. Stage of Producta mesoloba. |
The marine fauna of the Upper Carboniferous beds, which is so poorly represented in Britain, but is well developed in Spain, Russia, Asia and North America, is largely characterised by the abundance of foraminifers of the genus Fusulina and Fusulinella and of bryozoa of the genus Archimedipora. It is very desirable that the truly marine fauna of the Spirorbis limestone and other marine bands of the British Coal Measures should be carefully studied to see if they present any close relationship with that of the Gshellian beds[92].
[92] A good idea of the general characters of the Carboniferous fauna of Britain will be obtained from an examination of Professor Phillips' Geology of Yorkshire, Part I., and Mr (now Sir F.) McCoy's Carboniferous Fossils of Ireland, while the nature of the European fauna is well illustrated in Prof. de Koninck's well-known work Description des animaux fossiles qui se trouvent dans le terrain carbonifère de Belgique. For an account of the characters of the marine fauna of the Upper Carboniferous rocks the reader should consult the work on Geology and Palæontology published by the Geological Survey of the State of Illinois in 1866.