The shallow sea between Cape York peninsula and New Guinea is choked with innumerable coral reefs. By wind and wave action sandy islets have been built up on some of these reefs, and the coral sand has been enriched by enormous quantities of floating pumice. Wind-wafted or water-borne seeds have germinated and clothed the sandbanks with vegetation. Owing to the length of the south-east monsoon, the islands have a tendency to extend in a south-easterly direction, and consequently the north-west end of an island is the oldest, hence one sometimes finds that in the smaller islands a greater vegetable growth, or the oldest and largest trees, is at that end of an island; but in time the vegetation extends uniformly over the whole surface. The islands of the central division are entirely vegetated sandbanks.
The eastern division of Torres Straits includes the islands of Masaramker (Bramble Cay), Zapker (Campbell I.), Uga (Stephen’s I.), Edugor (Nepean I.), Erub (Darnley I.), and the Murray Islands (Mer, Dauar, and Waier), besides several sandbanks, or “cays.”
All the above-named islands are of volcanic origin. The first five consist entirely of lava with the exception of two patches of volcanic ash at Massacre Bay, in Erub, to which I have already referred. Mer, the largest of the Murray Islands, is composed of lava and ash in about equal proportions, while Dauar and Waier consist entirely of the latter rock. It is interesting to note that where the Great Barrier Reef ends there we find this great outburst of volcanic activity. It was evidently an area of weakness in one corner of the continental plateau of Australia. In pre-Carboniferous times the tuffs were ejected and the lava welled forth that have since been metamorphosed into the rocks of the Western Islands; but the basaltic lavas of the Eastern Islands belong to a recent series of earth movements, possibly of Pliocene age.
MAP OF TORRES STRAITS
Strictly speaking, to the three islands of Mer, Dauar, and Waier should the name of Murray Islands, or Murray’s Islands, be confined; but in Torres Straits the name of Murray Island has become so firmly established for the largest of them that, contrary to my usual custom, I propose to adopt the popular rather than the native name.
Mer, or Murray Island, is only about five miles in circumference, and is roughly oval in outline with its long axis running roughly north-east to south-west. The southerly half consists of an extinct crater, or caldera, which is breached to the north-east by the lava stream that forms the remainder of the high part of the island. This portion is very fertile, and supports a luxuriant vegetation, which, when left to itself, forms an almost impenetrable jungle; it is here that the natives have the bulk of their gardens, and every portion of it is or has been under cultivation. The great crescentic caldera valley, being formed of porous volcanic ash and being somewhat arid, is by no means so fertile; the vegetation, which consists of grass, low scrub, and scattered coconut palms, presents a marked contrast to that of the rest of the island. The slopes of the hills are usually simply grass-covered.
Fig. 1. The Hill of Gelam, Murray Island