plants. With a suitable temperature there is nothing to
prevent a luxuriant vegetation up to the pole, and the long continued day
is known to be highly favourable to the development of foliage, which in
the same species is larger and better developed in Norway than in the south
of England.

[79] _Geological Magazine_, 1873, p. 320.

[80] _Geological Magazine_, 1877, p. 137.

[81] _Manual of Geology_, 2nd Ed. p. 525. See also letter in _Nature_, Vol.
XXIII. p. 410.

[82] _Nature_, Vol. XVIII. (July, 1878), p. 268.

[83] "On the Comparative Value of certain Geological Ages considered as
items of Geological Time." (_Proceedings of the Royal Society_, 1874, p.
334.)

[84] _Trans. Royal Society of Edinburgh_, Vol. XXIII. p. 161. _Quarterly
Journal of Science_, 1877. (Croll on the "Probable Origin and Age of the
Sun.")

[85] _Philosophical Magazine_, April, 1853.

[86] It has usually been the practice to take the amount of denudation in
the Mississippi valley, or one foot in six thousand years, as a measure of
the rate of denudation in Europe, from an idea apparently of being on the
"safe side," and of not over-estimating the rate of change. But this
appears to me a most unphilosophical mode of proceeding and unworthy of
scientific inquiry. What should we think of astronomers if they always took
the lowest estimates of planetary or stellar distances, instead of the mean
results of observation, "in order to be on the safe side!"? As if error in
one direction were any worse than error in another. Yet this is what
geologists do systematically. Whenever any calculations are made involving
the antiquity of man, it is those that give the _lowest_ results that are
always taken, for no reason apparently except that there was, for so long a
time, a prejudice, both popular and scientific, against the great antiquity
of man; and now that a means has been found of measuring the rate of
denudation, they take the slowest rate instead of the mean rate, apparently
only because there is now a scientific prejudice in favour of extremely
slow geological change. I take the mean of the whole; and as this is almost
exactly the same as the mean of the three great European rivers--the Rhone,
Danube, and Po--I cannot believe that this will not be nearer the truth for
Europe than taking one North American river as the standard.

[87] "On the Height of the Land and the Depth of the Ocean," in the
_Scottish Geographical Magazine_, 1888.

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