The source of the cold stream of fresh water they did not find, for it came dancing down the dark ravine, which was choked with tree-ferns, creepers, and interlacing boughs laden with the loveliest orchids, and their progress was completely stopped when they had advanced some hundred yards or so. "The beginning of the curious features of the place," said Sir John as they sat down to their pleasant meal, gazing through an arch of greenery at the sapphire lagoon and the silver foam of the billows on the creamy reef half-a-mile away. Never did lunch taste more delicious to the rapidly invigorating boy, never was water fresher, sweeter, and cooler than that of which he partook. Then a good long hour's rest was taken as they all lay about listening to the hum of insects, the whistle, twitter, and shrieking of birds; and beneath it all, as it seemed, came the softened bass from the reef. "What do you say to a start back, Mr Bartlett?" said Sir John at last, as he glanced at his son, who had just risen and gone knife in hand to dislodge a cluster of lovely waxen, creamy orchids from a tree overhanging the pool. "I think we ought to be going soon, sir," said the mate. "Here, Jack, my lad, what's the matter?" cried the doctor, springing up, as he saw the lad holding the flowers he had cut at arm's length. "Ah! stand still! Don't move whatever you do." "Help, help!" shouted Edward. "Snakes! snakes!" "Down flat, my lads, quick!" cried the mate; and as the men obeyed he pointed out across the lagoon to where a great matting sail came gliding into sight, looking misty and strange as seen through the veil of foam hanging iridescent about the reef, and twice over rising up sufficiently for the long low hull of a great sea-going canoe crowded with men to come into sight. CHAPTER TWENTY ONE. AN ADVENTURE. Jack did not see the canoe, for his attention was taken up by the little serpent which had suddenly flung itself upon his hand, as he disturbed the cluster of flowers, and struck at his arm sharply--twice.