74 SECTIONAL ADDRESSES 
the accession of water to the desert region would permit of some increase 
in rainfall over the area. The land would therefore be ready for plant 
colonisation, but each element of the flora would have more or less an 
equal chance, and the more vigorous race would prove successful. It is 
in some such way I picture the conditions to the north and west of Britain 
—in Greenland if you will—during late Cretaceous and early Tertiary 
times. 
To an extent this will also account for Greenland as one distributing 
centre for the angiosperms at a later date ; and, in addition, the depression 
would encourage the chance of ocean currents from the south rendering 
the climate rather warmer during the later stages than during the earlier. 
In fact it would explain the climatic conditions in England up to the time 
of the London Clay deposits. 
THe TERTIARY FLORAS. 
While there is some admixture of the Tertiary and the older Mesozoic 
flora to be observed in one or two localities, on the whole the change 
comes with dramatic suddenness. So sudden, indeed, that attempts at 
possible explanations appear futile, for there is no evidence of any com- 
parable change in inorganic nature. Examination of the sediments 
deposited before and after those of the zone in which the change is ob- 
served do not indicate any cause for the phenomenon, nor can the corre- 
sponding igneous rocks, if available, give us any clue. But, and this, so 
far as we are concerned, is the most important feature of all, the whole 
basis of classification of the fossil plants is also changed. ‘This point is 
simply not appreciated by the average geologist, and, for that matter, it 
seems to have been tacitly ignored by the palzobotanist. What would 
we say to the mineralogist who classified minerals by their colour? It 
could be done; it has been done. ‘That was the basis of Werner’s classifi- 
cation, and we find men like Jameson defending it. Now there is no 
doubt that such a method would, now and again, be accurate—azurite, 
malachite, etc., have distinctive colours—but what faith would we have 
to-day in mineralogical conclusions based on such a scheme ? 
The classification of flowering plants is based on floral characters and 
fructifications—this is the result of the combined experience of botanists— 
and these characters depend on delicate structures produced at a particular 
season of the year, generally totally different from the vegetative parts of 
the parent plant, and developing in a very few days into a fruit that is also 
totally distinct from the other members of the plant that bears it. While 
the two end stages—the vegetative body and the seed—may be fairly 
persistent over a period of months, the flower may last only a few hours. 
Yet the floral characters are the basis of botanical classification. The 
chances of preservation of such delicate structures are very few (though 
they occasionally are found, as in the fine ashes of the Miocene Lake, 
Florissant, Colo.), and the chances of correlation with their parent plants 
are still fewer. With what are we left? The vegetative structures, 
definitely rejected by the botanist as bases of classification of flowering 
plants! We cannot get away from this position, that, as a matter of 
observation, the vegetative parts of flowering plants are not safe criteria 
