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:-- { Beds with _Spirifera fascigera_, _Spiriferina_ Gshellian { _Saranae_, &c. (with _Fusulina_ and { Beds with _Producta cora_, _P. uralica_, _Archimedipora_) { _Camarophoria crumena_, &c. { Beds with _Syringopora parallela_ and { _Spirifera striata_. Moscovian { Stage of _Spirifera mosquensis_. { Stage of _Spirifera Kleini_. { Coals, Sandstones and Shales with _Noeggerathia_ Lower Carboniferous { _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]. [Footnote 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.) M^{c}Coy'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.] CHAPTER XIX. THE CHANGES WHICH OCCURRED DURING THE THIRD CONTINENTAL PERIOD IN BRITAIN; AND THE FOREIGN PERMO-CARBONIFEROUS ROCKS.