Seward: The Jurassic Flora of Yorkshire. gl 
of our ability to draw conclusions as to climate from a com- 
parison of Jurassic and recent floras. Darwin wrote in a letter to 
Bentham in 1869, ‘I regret whenever a chance is omitted of 
pointing out that the struggle with other plants (and hostile ani- 
mals) is far more important’ than are soil and climate in deter- 
mining the distribution of plants. We are totally unable to 
estimate the significance and the far-reaching consequence of the 
advent of the highly elaborated type of plant represented by 
the flowering plants. It is such considerations as these which 
help us to realise the complexity of the factors concerned in the 
sequence of events which have happened since the fragmentary 
fossils of the Yorkshire cliffs played their part in the machinery 
of living forest trees, or contributed to the needs of lower- 
growing Cycads or still humbler plants. 
I now pass to the concluding section of my Address, namely 
a brief review of the relation of the Jurassic flora of the north- 
east of England to floras which flourished in other parts of the 
world during different phases of the Jurassic period. It is 
hardly necessary to point out that in treating of the geographical 
distribution of Jurassic floras, the application of the term 
Jurassic or even Inferior Oolite to floras from different regions 
does not carry with it the assumption of contemporaneity. 
All that we can do is to compare floras obtained from homo- 
taxial rocks (to use Huxley’s term) in order to ascertain 
whether or not there is any evidence for supposing that in 
the Jurassic era, as at the present day, there was a regional 
differentiation of the world into botanical provinces. It would 
involve us in a mass of detail were I to enter fully into this 
question, but by selecting a few genera of plants characteristic 
of the Jurassic flora of Yorkshire, and noting the records of 
their occurrence elsewhere, enough evidence may be put 
forward to furnish some justification for the belief that the 
Jurassic vegetation was remarkably uniform. In this incom- 
plete survey are included a few floras assigned to the Rhaetic 
or Liassic series which, though not referable with precision to 
a particular horizon, are clearly older than the Jurassic flora 
of Yorkshire. It is important to notice that in their general 
facies, Rhaetic floras do not differ very materially from those 
of the Liassic and Oolitic periods. Similarly, the floras obtained 
from rocks at the base of the Cretaceous system conform in 
general features to those of Jurassic age. The floras selected 
for brief consideration are the followi ing :—1—Yorkshire ; 
2—Bornholm; 3—Poland; 4—Turkestan; 5—Siberia ; ae 
Korea ; = Tepe: 8—Franz, Josef Land and Spitsbergen ; 
g—Greenland ; 1o—Oregon and Oroville ; 11—Louis Phillipe 
Land ; 12—India; 13—Australia. 
I can best illustrate the geographical range of some of the 
1911 Feb. 1 
