There was plenty to say about bird and insect as they went on, keeping just where the sand gave place to firm ground, for the birds were excessively tame, and gave evident proof that they were not much disturbed; while every now and then amid the lovely insects which thronged wherever there were flowers, appeared some magnificent butterfly, several inches across its wings, tempting Sir John to cease exploring for the sake of making captures. But everything was given up to the main object, and mile after mile was tramped, every step seeming to reveal some new beauty--peeps through the groves at the broad blue sea, or wonderful landscapes up ravines, with the mountain towering up behind. The natural history objects they encountered were plentiful enough. In fact very few steps were taken without something attracting attention. Lizards which seemed as they basked on pieces of the heated rock to have been cut out of glittering metal, till, at the jar of a footstep, or the shadow of any one cast across them, they darted away. In one place the doctor pointed out sinuous markings on the sandy ground which looked as if freshly made. "Yes, a snake," said Sir John, "and a good-sized one too." "How large?" said Jack with suppressed excitement. "Seven or eight feet long, I should say," replied his father. Jack looked with an expression of mingled dread and longing at the patch of dense growth into which the track led, and directly after Edward exchanged glances with him, the man's look seeming to say-- "I've marked down that spot, sir." Glen after glen was passed, every one full of beauty and interest, and at last they were brought up short by what looked like some huge pier running right across their way, down over the sands, and ending suddenly about a hundred feet out in the beautiful blue lake. At the first sight it seemed like some great landing-place or wharf, but there was no sign of handiwork about it, and the lad gazed at it in awe, as the doctor explained that it was the end where it had cooled and solidified in the lake of a huge lava-stream which had flowed down from the mountain, high up on their right. "But that means it must have run like so much liquid fire for miles." "Yes, that's exactly what it does mean, Jack," said Sir John; "six or seven or eight. We shall know some day, when we have explored the place." "And that will be like a high-road to the top," said the doctor, "only I'm afraid it would be a rather rough one." "We'll try it some day," said Sir John. "Rather hard for your boots, sir," said the captain. "Look at it: like glass, and as sharp in places." "Why, it must be quite fresh," said Jack. The captain smiled and shook his head. "But some of these pieces look quite bright," said Jack. "Yes; and these trees look quite green, and many of them may be a hundred or two hundred years old." "What has that got to do with it?" said Jack. "Oh yes, I see now: they would have been burned up. Of course."