We know much less about the vegetation—the plants and grasses—of the early ages of the world than of the animals; because plants rot away faster than bones and shells, and, besides, are less likely to be found in places where they would be preserved. A dead tree might be eaten up entirely by insects, as the white ants eat up fallen trees in a short time in tropical countries, and what is left of them crumbles away to fine powder and mixes with the soil. Immense trees are thus devoured now by millions of tiny insects no longer than your thumb nail, in India and Australia. No such thing as a whole and perfect fossil tree with every twig and leaf has been found; but then the coal beds are really great forests which have been buried for so long a time that they have quite altered in appearance. Still, among these coal beds we often find the bark, fruit, stems, and branches of trees very much like firs, and ferns, and huge club-mosses, which have the same shape they had when living, though they are quite black, and burn exactly like coal. But there were plants long before the coal forests lived, and many fossil sea weeds are found in the old sandstones and limestones in Wales and other places.[3] The Old Red Sandstone, whose position you can see below the coal in the table of succession of formations, page 42, does not give us many fossil plants, though fishes and shells are common. This rock is found in Scotland, Herefordshire, Devonshire, and Ireland, as well as other places, and is often more than 2,000 feet thick. It was not all formed in salt water we know, because many of the fossil fishes and shells it contains are fresh water kinds. It must all have been made of the pieces of still older rocks worn away by rivers and settled like a sediment in immense lakes, some of which were fresh water. Then, after the Old Red Sandstone, came a time when the limestones below the coal were laid down at the bottom of a vast sea, and here the remains of land plants are of course few. Then it seems there must have been a very long time when there were large continents all over the world raised above the seas, but not very much, and on these the forests grew which afterwards became coal fields. Until this time the plants had been mostly water weeds, reeds, rushes, and sea weeds, and it was not until England and Ireland became one continent, as they were once and covered with woods, that the great period of vegetation began.