In this part, the reader's first concern is to get a clear picture of the island's geography and the ship's position in that context. Much of this is discussed in Chapter 17 as Silver explains the chart to Smollett, and more is discussed in Chapter 18. Treasure Island, as Jim's description of Billy Bones' chart shows it in an earlier chapter, is a roughly rectangular or oval piece of land, narrower at the northern and southern ends than in the middle, and about five miles wide by nine miles from north to south. The ship has approached it from the northeast at the end of Part II. The three hills that the men see at that time are called after the three masts of a ship as seen from off the bow, "Fore," "Main," and "Mizzen"; the central one, "Mainmast," is also called "The Spy-Glass" because it is the tallest and it was from here, Silver says, that a watch was kept when earlier pirates stopped at the island. During the night, the Hispaniola continues to sail in a southwesterly direction, so that when Jim wakes in the morning he sees the eastern shore of the island from a point somewhat south of its center.
Captain Smollett, following Silver's direction, has decided to go to the southern tip of the island, which is separated by a strait a little less than a mile wide from an islet (called "Skeleton Island"); the strait is so shallow that at low tide this islet is all but connected to the main island. Silver says there is a strong current moving westward across the southern end and then moving northward up Treasure Island's western shore, but there is no current in the strait, so it is in the shallow strait that they will take the ship to be anchored. As there is no wind this morning, they cannot sail into the strait. Thus the men have to get in boats and row, towing the ship a few miles farther south, around the southeastern corner of the main island, and then westward into the strait to the anchorage.
