GEOLOGY OF TORRES STRAIT. [From the Nautical Magazine.]

New Zealand Spectator and Cook's Strait Guardian, Volume IV, Issue 304, 28 June 1848, Page 3

GEOLOGY OF TORRES STRAIT. [From the Nautical Magazine.]

We have been favoured with the following interesting remarks on the Geology of Torres Strait, from the pen of Mr. Jukes, the Naturalist, who accompanied the Surveying Expedition commanded by Captain Blackwood, and as the subject is intimately connected with the hydrography of that remarkable locality, we gladly give these remarks a place in our pages. There are two geological features of some importance to the hydrography of Torres Strait and its neighbourhood. The first is that the rocks which form the high land of the north-east coast of Australia, stretch also across Torres Strait in a narrow band, running nearly north up to the shores of New Guinea. Along this band there rise steep and rocky islands, of precisely the same geological features as the hills of the main land to the southward. This narrow band forms a western boundary to the Great Barrier coral reefs just as much as does the dry land to the southward, since no " independent coral reefs" obtrude upon it, and the only coral-formed masses to be found in it are small " fringing reefs" adhering to the shores of the islands. From the knowledge of this fact two questions arise : Are the reefs seen by the Hormuzeen and Chesterfield to the north-west of this band true coral reefs, or are they only shoals of sand, mud, or other materials ? Of what are the islands called Duncans Archipelago composed ? If these latter are not coral islands, and I believe they are not, it is probable that deep water channels (8 or 10 fathoms) may be found between or around them, unless those channels should be blocked up by the more than usual extension of the " fringing reefs." I The second feature is the sudden ending of the coral reefs of the Great Barrier to the northward, and their reluctance to approach that part of the coast of New Guinea, composed of alluvial materials, and traversed by fresh water channels. This is a well known character of coral reefs, which results from the incapacity of the polypi to live in sea water charged with mud, or all mingled with fresh water. The nearest patch of coral to this coast, the fringing reef of Caedha or Bramble Key, is composed chiefly of a different species of coral from that forming the great reefs to the southward. Now, if the reefs seen by the Hcrmuzeen and Chesterfield are really coral reefs, (and the extension of the Warrior Island reef renders this probable,) a hydrographical deduction may be drawn from these facts : — namely that none of the drainage of this part of Guinea disembogues on the coast near Talbot Island, but is all thrown into the sea to the northward of Bampton Point. This is also rendered probable by the other fact of the rocks forming the north and south ranges of the Australian coast stretching across Torres Strait, towards this part of New Guinea, since if this great rib of rocks no longer rises into hills in that country, it will at least tend to do so for some distance before its effect on the surface of the ground is utterly lost, and probably form land above the average level of the surrounding country, and thus deflect the drainage to the northward and eastward. The fact of the Murray Islands, together \i ith Erroob or Darnley Island, and Bramble Key, being all composed of volcanic rocks, renders it probable that Airds Hill is also

volcanic. In that case a range of volcanic hills is very likely to proceed from the volcanic range of the north coast of New Guinea, and strike the south coast somewhere to the eastward,* about 146* or 147*. These would also deflect the drainage of that country in the direction of that part of the south coast of New Guinea which lies between the meridian of 143* and 145' E. All the T-nown geological features, then, of Torres Strait and its neighbourhood, go to make it probable that the drainage of a very large part of New Guinea disembogues on the tract of coast indicated, and show the reasons of its doing so. J. Beete Jukes.

* This anticipation seems to have been realised so far as the hills go (whatever may be their nature) by the high land seen, I understand, by Lieut. Yule, in that nfcighbourhood.