served point, according to H. Potonié,[1] to tropical forms, amongst other reasons, because of their rapid growth and the size of the leaf-frond, and on account of the absence of annual rings, the affinity with families that now have their home in the tropics, the frequency of tree- and climbing-ferns and the formation of the fructification on the stem itself, “cauliflorescence,” (which now only occurs in the tropics) in the Calamariaceæ, certain Lepidodendraceæ and the Sigillariaceæ. Some years ago it was thought by many (Ramann, Frech and others) that the formation of peat was connected with low temperature, and was impossible in the tropics because the processes of decomposition are much more powerful in those regions. This was quite natural so long as no recent bogs were known from the equatorial belt of rains. This, however, has been shown to be erroneous by the discovery of a great bog in the eastern portion of Sumatra, on the northern bank of the River Kampar; here the exclusion of atmospheric oxygen effected by the covering of water is sufficient to check decomposition and to produce peat. Since then further peat-bogs have been discovered in Ceylon and Equatorial Africa. Therefore the former very lively discussion on the tropical nature of our coal measures can be considered as having been settled. As is shown by Fig. 17, this girdle of coal measures lies exactly on the great circle which occurs about 90° from the centre of the area of glaciation. That this happy solution is only rendered possible by the displacement theory is shown by the annexed map of Kreichgauer, which is given for the sake of comparison (Fig. 18). Just as in the case of the
- ↑ H. Potonié, “Die Tropensumpfflachmoornatur der Moore des productiven Karbons,” Jahrb. d. Kgl. Preusz. Geol. Landesanstalt., 33, Teil 1, H. 3, Berlin, 1909.—H. Stremme, Über tropische Moore, “Gæa,” 45, No. 11, 1909.
