How it came to be discovered is another thing we do not know, or by what race. It is very likely that it was made by many different peoples, at different times in the world's history. Over and over we find that some race which had gone far along the road to civilisation, would be swept away by savage tribes and its discoveries lost for many centuries. We know this, because sometimes we find, when digging in the earth, the remains of savage peoples, with thick skulls and rude weapons, and under these are the skulls and polished weapons and ornaments of a much more highly civilised race. The road which man followed in his progress toward the civilisation we have to-day did not run smoothly upward, like a path up a hill, but dipped up and down and around in many circles, always rising a little higher, however, as the ages went by.
It is thought that the sea people first discovered glass. Ordinary glass is made of lime, soda-ash and sand, three very common substances. Because sand is the thing most needed in making glass, we think it must have been discovered by a people living on the seashore. It must have been first made by accident, because man could not have set out to discover something he did not know anything about.
The most common story about the first glass is that it was made by some sailors belonging to the Phœnicians, one of the early sea-going tribes living on the shores of the Mediterranean Sea. It is supposed that these sailors, building a fire on the seashore to cook food, may have propped their pots up on pieces of limestone, which furnished the lime, just as the beach furnished the sand, and the fire, the ash and the heat. Probably they found in the ashes of their fire a hard, greenish lump of glass. They did not know what it was, of course, but carried it away because it was clear and bright and pretty in colour, like a jewel. Wiser men, hearing their story, may have learned in this way how to mix sand, lime and soda-ash together and by heating it form glass.
The earliest things made of glass were coarse beads, and little bottles and vases. Later on, man came to make very beautiful glass vases and bowls and drinking cups, such as those found in ancient tombs in Egypt, and in the ruins at Troy, and on the Island of Cyprus. These cups and bowls and other objects are tinted the most wonderful colours, blue and green and gold, like the feathers of a peacock. It is said that the ancient Egyptians knew how to make glass that would not break, so that a vase, dropped to the floor, instead of being shivered to pieces, would be only bent out of shape. This secret, like the way the Egyptians had of hardening and tempering copper, has been lost, and the most skilful glass makers to-day could not make glass like that.
CHAPTER XXI
THE END OF THE STONE AGE
During all these long centuries, many, many thousands of years, the people from the valley where Adh and his wife first lived had been spreading far out over the surface of the earth. Many boats and canoes, carried by storms from the country of the sea people, were driven to other countries, and all around the shores of the sea new tribes were springing up. Century after century, as these tribes became larger, and game grew scarce, new bands of adventurers wandered off into the wilderness inland, and from the tribes they formed still other bands wandered away. Some crossed great lakes and seas in boats, others drifted down mighty rivers for hundreds, and even thousands, of miles, on rafts. Mountain ranges were crossed to find new hunting grounds, and new tribes were formed, which in their turn sent out other bands of adventurers. During all this time the face of the earth was changing. Great glaciers from the frozen north crept southward century after century, grinding the surface of the rocks like giant ploughs. Earthquakes and floods caused new continents to rise where before there had been only seas, or made seas, in places where there had been dry land. Mother Nature's new race of men had to fight the heat and the cold, the storms and the sea, as well as the fierce animals which were always ready to attack them, but in spite of all these things, they spread and grew, year after year, until the earth began to be covered with them.
They did wonderful things with their tools of stone. Remains of their work are found in many places, tens of thousands of years old. On the Island of Malta, in the Mediterranean Sea, there has been found an underground temple of great size, with many arched and vaulted rooms, beautifully carved, all of which were cut out of the solid rock with axes and chisels of flint. In other places wonderful temples, tombs and buildings of various sorts have been discovered, built of great cut stones, and we wonder how such huge rocks could ever have been squared and polished so beautifully with nothing but tools of stone.