re of their stems. Thus, in the rich cretaceous plant-beds of the
Dunvegan series, we have beech-nuts associated in the same bed with
leaves referred to _Fagus_. In the Laramie beds I determined many years
ago nuts of the _Trapa_ or water-chestnut, and subsequently Lesquereux
found in beds in the United States leaves which he referred to the same
genus. Later, I found in collections made on the Red Deer River of
Canada my fruits and Lesquereux's leaves on the same slab. The presence
of trees of the genera _Carya_ and _Juglans_ in the same formation was
inferred from their leaves, and specimens have since been obtained of
silicified wood with the microscopic structure of the modern butternut.
Still we are willing to admit that determinations from leaves alone are
liable to doubt."--_The Geological History of Plants_, p. 196.]

[Footnote 192: Sir J. William Dawson's _Geological History of Plants_,
p. 18.]

[Footnote 193: "On the Origin of the Flora of the European Alps," _Proc.
of Roy. Geog. Society_, vol. i. (1879), pp. 564-588.]

[Footnote 194: Systematic Review of our Present Knowledge of Fossil
Insects, including Myriapods and Arachnids (_Bull. of U.S. Geol.
Survey_, No. 31, Washington, 1886).]

[Footnote 195: For the facts as to the early appearance of the above
named groups of reptiles I am indebted to Mr. E. Lydekker of the
Geological Department of the Natural History Museum.]

[Footnote 196: According to Professor Marsh this creature was 50 or 60
feet long, and when erect, at least 30 feet in height. It fed upon the
foliage of the mountain forests of the Cretaceous epoch, the remains of
which are preserved with it.]

[Footnote 197: For fuller details, see the author's _Geographical
Distribution of Animals_, and Heilprin's _Geographical and Geological
Distribution of Animals_.]

CHAPTER XIV

FUNDAMENTAL PROBLEMS IN RELATION TO VARIATION AND HEREDITY

Fundamental difficulties and objections--Mr. Herbert Spencer's
factors of organic evolution--Disuse and effects of withdrawal
of natural selection--Supposed effects of disuse among wild
animals--Difficulty as to co-adaptation of parts by variation
and selection--Direct action of the environment--The American
school of evolutionists--Origin of the feet of the
ungulates--Supposed action of animal intelligence--Semper on the
direct influence of the environment--Professor Geddes's theory
of variation in plants--Objecti