"In this little transaction," said Frank, "you can see the use of money. There was no circulating medium where Captain Cameron was trying to hire the boat, and consequently a great deal of time was lost in making the various negotiations." "You will find," said the Doctor, "that the most of the people of Africa have some sort of circulating medium; we have already seen how the tusk of the elephant is a standard of value, and how shells, beads, cloth, and other African goods have a more or less fixed rate. There are few places on the continent where it is necessary to traffic in the manner described by Cameron, and the number is steadily diminishing." [Illustration: ARMS AND ORNAMENTS.] CHAPTER XXVIII. THE ALEXANDRA NILE.--FRED'S DESCRIPTION OF THE WEST COAST OF AFRICA. From Dumo they continued their course to the southward, passing a crescent-shaped bay, bordered by a dense forest and backed by a semicircle of hills. Beyond this bay they turned a headland, and a few minutes afterward Fred observed that the water was of a darker color than they had hitherto found it. "According to the map," said the Doctor, "this is the Bay of Usongora; the Alexandra Nile empties into it, and its waters, rolling through an alluvial country, are charged with earthy matter, which gives it the color you perceive." Frank wished to ascend the river; but the Doctor said they could not do so, as it would not be in accordance with their agreement with M'tesa to attempt any explorations. They passed near enough to the mouth of the river to see that it was about one hundred and fifty yards wide, and by the way the water flowed into the lake there was evidently a considerable volume of it. Stanley ascended the river about three miles, and said he found the current so strong that his boats made very slow progress, and he was obliged to give up the attempt. The plain on each side of the river in the portion near the lake is from five to ten miles wide, and in the season of high water it is completely overflowed. The Alexandra Nile is the largest of the affluents of the Victoria N'yanza; the second largest river flowing into it is the Shimeeyu, and the two streams together are estimated to be nearly equal to the volume of water that passes Ripon Falls. Most of the natives call the Alexandra Nile "the mother of the river at Jinja," or the Ripon Falls. [Illustration: VIEW OF THE UPLANDS IN KARAGUÉ.]