70 SECTIONAL ADDRESSES 
a tropical one, and (b) if the South Pole were in the Indian Ocean the North 
Pole would come out in N.W. Mexico, and no sign occurs there of Permo- 
Carboniferous glaciation. Even on the best arrangement of these locali- 
ties to suit Wegner’s hypothesis of continental drift, some evidence of 
cool conditions should be found in the rocks of that area; hot, arid 
conditions, however, are indicated rather than cold. 
The mixing of northern types in the Glossopteris floras, as shown by 
several recent papers, has some bearing upon the question of the complete 
isolation of Gondwanaland from the northern continents ; so also has the 
discovery of still other floras of Permo-Carboniferous age—the Giganto- 
pteris flora of China and Korea; the Angaraland flora of Siberia; and the 
Upper Permian flora of the Grand Canyon of the Colorado. But, until 
more is known of these latter, hypothetical re-arrangements of continents 
and oceans are rather premature, though, of course, they are interesting 
exercises of ingenuity. The Gigantopteris flora 4° had an admixture of 
forms more common in the Mesozoic rocks, as also had the Angaraland 
flora. The flora of the Grand Canyon deposits,*! too, had Mesozoic 
characters. It would be interesting if the quantitative method of David 
Davies could be applied to all these floras to determine which plants 
were really abundant, and which were rarities. There is one area at least 
where this could be done, namely, at Wankie in Southern Rhodesia. 
Several of us in this room will remember the absolute preponderance of 
Glossopteris on the horizon from which we collected in the field at Wankie 
in 1929, as well as in the samples brought to us at the Mine Offices through 
the good graces of the manager. The ‘ northern forms’ were conspicu- 
ous by their rarity. It is too much, at present, to expect these intensive 
studies to be conducted in the areas in question, but such ecological 
researches will have to be attempted before we can say that these floras 
may be used as confidently for zonal, or other geological and palzogeo- 
graphical conclusions, as we can employ the Coal Measure floras of N.W. 
Europe and Eastern America. 
Generally speaking, the Paleozoic floras occupy the greater part of the 
attention of geologists, and the reason is not far to seek. If fossil plants 
are to be used at all in zonal work, they must be used in areas where there 
is a practical demand for such zoning, and where plants are abundant. 
Now we know that there are coal seams of Mesozoic and Tertiary age of 
very great extent, and of enormous potential value, but they have not 
been exploited so thoroughly as the late Paleozoic coals, and consequently 
the associated floras have not yet received the attention they merit. But 
the work of du Toit, Walkom, Halle and others is gradually making us 
better acquainted with these floras. 
Mesozoic Fioras. 
_On the other hand, many important results, from a botanical point of 
view, have been obtained from the examination of the Triassic and 
Jurassic plants ; and the Botany School, Cambridge, has been especially 
40 See Seward, Plant Life through the Ages. 41 D. White. 
