This fact is a key to the culture of the Bronze Age. Widely separated communities, destitute of a knowledge of metals, would instinctively make use of stone. In this case uniformity of type would not imply community of knowledge. But a knowledge of metals is altogether different. It is wonder enough that one community should have hit on the invention of bronze. The chance would be against its independent discovery in widely separated areas. They would be more apt to chance on the production of some other metal. Thus; tribes in the interior of Africa are said to have passed direct from the Stone to the Iron Age, a knowledge of bronze not having been carried to them. We are thus able to form a true conception of the Bronze Age. It did not prevail over the world at the same time. Indeed, as we shall subsequently see, there is every reason to suppose it spread very slowly, and that it still lingered in Central and Northern Europe long after its use had been abandoned for that of iron in the South. Neither, when it was first introduced, did it put a stop to the use of stone. It was necessarily costly, and on its first appearance in a country, brought hither by trade, could only be afforded by rich and powerful chiefs and warriors. As time advanced, and they learned to make it cheaper, and each country took up its separate manufacture, it would gradually supersede stone. But bronze was never cheap enough to drive out the use of stone altogether. This only occurred when the art of working iron was discovered. We shall learn that the knowledge of bronze, while a very important and distinguishing phase of culture of the Bronze Age, was not its only characteristic. It was distinguished by the arrival and spread of the Aryan races, by a great extension of commerce, by more refinements in the comforts of life, by the increasing strength of government, which in after ages flowered out in the mighty nations of antiquity, and rendered historic, civilization possible. Some facts stand out with great prominence. The origin of this culture is lost in the very night of time. We may be sure that it goes back to a profound antiquity, and that it extended over a long series of years.