at one time many people believed that the middle of africa was a sandy desert, where nothing could live but camels and ostriches. but they were mistaken. the great traveller, david livingstone, journeyed into this unknown country, and he found that it was not a desert but a beautiful land, where many tribes of black people dwelt. he also saw that these people were often seized by strangers, and taken away to be sold as slaves. this sight filled him with sadness, and he made up his mind to put a stop to this cruel traffic. he worked hard, tracing the courses of the rivers, finding the best tracts of land, and teaching the natives.