nery of a district
may be well learnt from a very clever and interesting little book of
Professor Geikie's, on 'The Scenery of Scotland, as affected by its
Geological Structure.' How far the plants and trees affect not merely
the general beauty, the richness or barrenness of a country, but also its
very shape; the rate at which the hills are destroyed and washed into the
lowland; the rate at which the seaboard is being removed by the action of
waves--all these are branches of study which is becoming more and more
important.

And even in the study of animals and their effects on the vegetation,
questions of really deep interest will arise. You will find that certain
plants and trees cannot thrive in a district, while others can, because
the former are browsed down by cattle, or their seeds eaten by birds, and
the latter are not; that certain seeds are carried in the coats of
animals, or wafted abroad by winds--others are not; certain trees
destroyed wholesale by insects, while others are not; that in a hundred
ways the animal and vegetable life of a district act and react upon each
other, and that the climate, the average temperature, the maximum and
minimum temperatures, the rainfall, act on them, and in the case of the
vegetation, are reacted on again by them. The diminution of rainfall by
the destruction of forests, its increase by replanting them, and the
effect of both on the healthiness or unhealthiness of a place--as in the
case of the Mauritius, where a once healthy island has become
pestilential, seemingly from the clearing away of the vegetation on the
banks of streams--all this, though to study it deeply requires a fair
knowledge of meteorology, and even of a science or two more, is surely
well worth the attention of any educated man who is put in charge of the
health and lives of human beings.

You will surely agree with me that the habit of mind required for such a
study as this, is the very same as is required for successful military
study. In fact, I should say that the same intellect which would develop
into a great military man, would develop also into a great naturalist. I
say, intellect. The military man would require--what the naturalist
would not--over and above his intellect, a special force of will, in
order to translate his theories into fact, and make his campaigns in the
field and not merely on paper. But I am speaking only of the habit of
mind required for study; of that inductive habit