Joan and Paul obeyed; though in his record of the aventure he never described the details of their ascent. A few minutes later they were perched beside the child near the rounded top of the ilex. ‘It’s fearfully rickety,’ Joan said breathlessly. ‘But there’s no danger,’ whispered Nixie, ‘because this is an evergreen tree, and it doesn’t go with the others.’ ‘How—“Go with the others?”’ asked the two in the same breath. ‘Trees,’ answered the child. ‘They’re emigrating. Look! Listen!’ ‘Migrating,’ suggested Paul. ‘Of course,’ Nixie said, poking her head higher to see into the sky. ‘Trees go away south in the autumn just like birds—the real trees; their insides, I mean——’ ‘Their spirits,’ Paul explained in his lowest whisper to Joan. ‘That’s why they lose their leaves. And in the spring they come back with all their new blossoms and things. If they find nicer places in the south, they stay, that’s all. They—die. Listen—you can hear them going!’ High up in that still autumn sky there ran a sweet and curious sound, difficult to describe. Joan thought it was like the rustle of countless leaves falling: the tiny tapping noise made by a dying leaf as it settles on the ground—multiplied enormously; but to Paul it seemed that sudden, dream-like whirr of a host of birds when they wheel sharply in mid-air—heard at a distance. There was no question about the distance at any rate. ‘Are they just the trees of our woods, then?’ asked Joan in a whisper that held delight and awe, ‘or——’ The child laughed under her breath. ‘Oh, no,’ was the reply, ‘all the South of England below a certain line meets here. This is one of the great starting-places. It’s just like swallows collecting on the wires. Some big tree, higher than the rest, gives a sign one night—and then all the other woods flock in by thousands. Uncle Paul knew _that_!’ There was a touch in her voice of something between scorn and surprise. ‘Did you, Uncle Paul?’ Joan asked. He fidgeted in his precarious perch. ‘I write the Record of it all, so I ought to,’ he answered evasively. And high up in the autumn sky, now darkening, ran on that curious sweet sound. Across the heavens, silvery in the coming moonlight, they saw long feathery clouds drawn thinly from north to south, known commonly as mares’ tails. ‘Those are the tracks they follow,’ whispered Nixie. ‘Look! Now you can see them—some of them!’ Her voice was so thrilled that it startled them. But for the fact that they were in the Crack where nothing can be ever ‘lost,’ both Paul and Joan might have lost their hold and their seats—to say nothing of their lives—and crashed downwards through the branches of that astonished ilex tree. Instead, they turned their eyes upwards and stared.