300 Geographical Distribution of Plants 
figure.” I can only summarise the conclusions of a technical but 
masterly discussion. “The broad general features of the distribution 
of continent and ocean can be regarded as the consequences of simple 
causes of a dynamical character,” and finally, “As regards the contour 
of the great ocean basins, we seem to be justified in saying that the 
earth is approximately an oblate spheroid, but more nearly an 
ellipsoid with three unequal axes, having its surface furrowed 
according to the formula for a certain spherical harmonic of the 
third degree’,” and he shows that this furrowed surface must be 
produced “if the density is greater in one hemispheroid than in the 
other, so that the position of the centre of gravity is eccentric®.” 
Such a modelling of the earth’s surface can only be referred to a 
primitive period of plasticity. If the furrows account for the great 
ocean basins, the disposition of the continents seems equally to 
follow. Sir George Darwin has pointed out that they necessarily 
“arise from a supposed primitive viscosity or plasticity of the earth’s 
mass. For during this course of evolution the earth’s mass must 
have suffered a screwing motion, so that the polar regions have 
travelled a little from west to east relatively to the equator. This 
affords a possible explanation of the north and south trend of our 
great continents*.” 
It would be trespassing on the province of the geologist to pursue 
the subject at any length. But as Wallace’, who has admirably 
vindicated Darwin's position, points out, the “question of the per- 
manence of our continents...lies at the root of all our inquiries into 
the great changes of the earth and its inhabitants.” But he proceeds: 
“The very same evidence which has been adduced to prove the 
general stability and permanence of our continental areas also goes 
to prove that they have been subjected to wonderful and repeated 
changes in detail®.” Darwin of course would have admitted this, for 
with a happy expression he insisted to Lyell (1856) that “the 
skeletons, at least, of our continents are ancient’.” It is impossible 
not to admire the courage and tenacity with which he carried on the 
conflict single-handed. But he failed to convince Lyell. For we 
still find him maintaining in the last edition of the Principles: 
“Continents therefore, although permanent for whole geological 
epochs, shift their positions entirely in the course of ages*.” 
Evidence, however, steadily accumulates in Darwin’s support. 
1 Report of the 77th Meeting of the British Association (Leicester, 1907), London, 1908, 
p. 431. 
2 Ibid. p. 436. 3 Ibid. p. 431. 
4 Encycl. Brit. (9th edit.), Vol. xxi. ‘‘ Tides,” p. 379. 
5 Island Life (2nd edit.), 1895, p. 103. § Loe. cit. p. 101. 
? More Letters, 11. p. 135. 
® Lyell’s Principles of Geology (11th edit.), London, 1872, 1. p. 258. 
