Fuels and foods are also alike in another respect; and that is, that, no matter how much they may differ in appearance and form, they are practically _all the result of life_.

This is clear enough as regards our foods, which are usually the seeds, fruits, and leaves of plants, and the flesh of animals.

It is also true of the cord-wood and logs that we burn in our stoves and fireplaces.

But what of coal and gasoline?
They are minerals, and they come, as we know, out of the depths of the earth.

Yet they too are the product of life; for the layers of coal, which lie sixty, eighty, one hundred and fifty feet below the surface of the earth, are the fossilized remains of great forests and jungles, which were buried millions of years ago, and whose leaves and branches and trunks have been pressed and baked into coal.