In the references to the different views held on the subject of past climates which have been given in the historical sketch, we have seen how much attention has been paid to the Carboniferous period, and how general has been the opinion that the Coal period climate was mild, if not tropical, and very uniform; not only in the absence of any great variation in temperature during the year, but uniform also in the sense of geographical distribution, without any indications of climatic zones or botanical provinces. The suggestion too of an abnormal amount of carbonic acid gas in the atmosphere of the Carboniferous forests has had many supporters.

To consider, first, some of the arguments which have led to these conclusions, and then discuss somewhat fully the view recently advanced that there is reason to believe the climate was by no means tropical, and that evidence is not wanting in favour of the existence of Carboniferous or Permo-Carboniferous botanical provinces.

An abstract of the views held by Grand'Eury, Saporta and others will serve to shew the main arguments brought forward to support the opinions generally held as to the Coal-period climate.

Grand'Eury does not overlook the difficulty of drawing conclusions as to climate from analogy, in the comparison of fossil and recent plants. The Marattiaceæ—so abundant in Carboniferous times—may, he suggests, have been capable of living under very different conditions than those most favourable to the present members of the family.