It is hard to realise that these mighty sea-walls are indeed the work of microscopic insects,—star-like creatures, invisible to the naked eye; but so it is. It is said they cannot live at a greater depth than thirty fathoms, yet the height of the coral-wall is in many cases double or treble this measurement, and in some cases a sheer descent of two hundred fathoms has been found. The inference is, that many of these isles, as well as the ocean-bed from which the coral rises, are gradually subsiding, and the insects are continually working upwards. In some cases the island has altogether disappeared, and there remains only a circular or crescent shaped reef, perhaps fringed with cocoa-palms, encircling a calm lagoon of clear green water, the sea all round being of the deepest blue. These are called _atolls_, and are sometimes many miles in circumference. Some scarcely rise above the water-level, and only a ring of white coral sand betrays their existence. The coral-reef gives us various hints of the rise and fall in the level of the ocean-bed, for while some islands have wholly disappeared, others are even now emerging from the waters. In some groups coral-cliffs have been found forty feet above the water-level—in other words, above the height where the insect could live, thus showing clearly that these rocks have been gradually upheaved. But in the Fijian group there are few islands which are not almost encircled by a barrier-reef of considerable depth, which would seem to indicate that they are actually subsiding. However, the process is likely to be a slow one, and a matter of no great moment to the present generation, or their successors for many years to come. I have spun a longer yarn than I intended, but it will help you to realise the sort of things that I am daily looking at, and will make the boys wish they were with me. * * * * * _Monday, 4th October._ DEAR JEAN,— ... I have just come in from such a scramble. Certainly those hills of Ovalau are most tantalising. From the sea they do look so attractive, and not particularly difficult to ascend; but when it comes to the attempt, you find that even in the rare instances where the semblance of a footpath exists, it takes a very good scrambler to follow it, over great boulders of rock, or up almost perpendicular banks of soapy mud. Should you attempt to leave the path, you find it almost impossible to force a passage through the dense underwood; and even the tracks, which from the sea look like grass, turn out to be tall reeds, reaching far above your head, and matted together with strong vines (which totally prevent your advance), and large spiders’ webs, which cling to your face and hair. Still, it is worth a considerable exertion, for the reward of at length reaching some point whence you can look down on the lovely sea and all the far-away isles.