Another rock of this time is called conglomerate, or mixed stone. Some call it “pudding-stone,” and say it looks like a pudding full of plums and lumps of suet. Such stone is very common, various kinds of pebbles and rocks being held together as if they had been baked or boiled into one mass. Near the conglomerate we sometimes find limestone full of tiny broken shells, and also beds of marl. Marl is a rich greenish earth, which crumbles easily and is valued for enriching cultivated lands.[13] All these varieties of rock are interesting when we study them, and can read the stories they tell of long-gone ages, of fire, volcanoes, earthquakes, floods, storms,--where strange animals and plants lived and died. Do we ever stop to think what a treasure-house of wonders and of choice and beautiful things the earth is? There are sands filled with grains of pure gold, and rocks where gold glows in grains and veins and nuggets. I have seen lumps of silver-bearing rock which look as if in some age of heat the pure silver had melted, boiled, and bubbled until now it lies in the stone in curious shapes, like balls, and stars, and chains, and moss, and tiny trees,--all fantastic and pretty forms. There are mines where diamonds, and rubies, and garnets, and sapphires lie hid as if the gnomes, or fabled earth-spirits, had stored them away. What crystals shine among the rocks, and red bands of carnelian glow, and purple amethysts and vivid carbuncles blaze! Kings have rooms full of such treasures kept for show; but the silent earth hides in her bosom many more and far richer jewels. Come here, and let me show you just one marvel made in the earth in some of these long building periods, when heat was working wonders. Since you have been handling all these minerals and curiosities your hands are dirty. Take this towel and wipe them. Look at the towel. What do you see? “Just a coarse cotton towel,” you say; “nothing fine about that.” “Very well. Have you wiped your hands? Here, let me throw the towel into the fire.” You stare at that. “Do you always burn your towels?” you ask.