It was five o'clock when the boys passed over the low banks of the Niger River.  By seven they were in the heart of the wild, level territory of Sokoto, skimming over vast expanses of plume-like grasses and extensive marshes and swamps.  Strange birds of enormous size flew up out of the morasses, startled at the sight and sound of the airplane.  Some tried to follow it, evidently to give it battle, but the swiftest of them were hopelessly outdistanced before they were well started.