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2 corrections, most recently by shutcheon - Show corrections

OBSIDIAN BUTTONS.

AN AUSTRALIAN RIDDLE.

By F. CHAPMAN (Assoc. Linn. Soc.,

London.)

From the time when Darwin, in 1844,  

described and figured an "obsidian bomb"     found "on a great sandy plain between the     Rivers Darling and Murray . . . at a dist- ance of several hundred miles from any     known volcanic region," these curious ob- jects have defied all efforts to satisfactorily explain their mode of origin.

Obsidianites, as R.H. Walcott has named     them in his classic description, are widely distributed over Australia and Tasmania. They generally occur in the open plains or in the beds of streams, and often far away

from any volcanic vent; so that had they been produced by volcanic action we should   have to call in some theory of aerial carriage by winds, as Twelvetrees and Pettero have         already hypothecated for the Tasmanian ex- amples, which "only required that the molten spray should have been ciarried by winds as far as Tasmania and Australia."

Obsidianites are commonly ball shaped sometimes with a flattened equator; occa- sionally they are split to reveal a flattened convex interior and an external flange-like   rim. Others have a dumb bell form or even cylindrical shape, with wedge-shaped ends.     One of the most remarkable though not     unique forms is the hollow sphere, upon   which has been founded the bubble theory by E. J. Dunn, strongly supported by Dr. Thorp, of Perth. That all these different shapes have been made by rotation in the air is proved by numerous instances of simi- lar bodies formed from molten material.  

In the great volcano of Kilauea in the Pacific, there occur masses of lava drawn   out into fine filaments. So thread like are these that the birds use them for nestmak- ing. The filaments are intermingled with glassy blebs. When these blebs are sorted over they are seen to comprise almost all the forms taken by the obsidianites. An interesting observation bearing on this sub- ject may be made from a railway train, if one is not averse from seating himself facing the engine and in the forword carriage. By placing a newspaper upon the knees, after a     time quite a quantity of fused coke from the smoke-stack will be found on the paper. It this is examined with a lens it will be seen that many of the shapes of obsidianites are there represented in minature. In the same way slag wool, which is produced by passing powerful jets of steam through molten slag or granite shows rounded and elongated blebs like the obsidianites dis- seminated through the mass. That, in the case of obsidianites, rotation of the material in the molten state took place is evident from the above experimental comparisons.   As Spencer and Gillen have written, in "Across Australia," the shape of these ob-   sidian bombs is just that which would be assumed by a small mass of molten vitreous material falling through the air and rotating

is it fell.

Comparatively recently Dr. Thorp, of

Western Australia has written about these remarkable "buttons," and advocating the bubble theory of Mr. Dunn, elaborates the method by which they may have been formed. He supposes volcanoes situated in the East Indies or Northern Australia   whose craters contained a thoroughly plas- tic glassy lava of the correct composition, wherein bubbles of highly superheated seaim or other gas rise with considerable force, carrying with them a thin pellicle or bubble of the lava with a bleb attached."

The idea of their being carried up "several miles" appears to rule this theory out of court, for some of the bombs are quite large, and especially so are those with the cavities. A useful feature of Dr. Thorp's   paper is the list of localities he gives where "Australites" have been found, viz., Queens- land (3), New South Wales (13), Victoria (36), Tasmania (29), South Australia (12), and Western Australia (33).

In common with all primative peoples the     Australian aborigine shows a veneration for unusual natural objects, and it is therefore not surprising to learn that the aborigines of Salt River, King George's Sound, prize these obsidian buttons. According to a correspondent of Professor R. Tate they     believe the possessor to "bear almost a charmed life, and is able also to cure sick people of my complaint they may be   afflicted with, as also to bewitch their enemies, or anyone with whom they have a grievance, tormenting them with all kinds of diseases and finally destroying life it- self." Mr. Canham of Stuart's Creek, wrote, in regard to one of these obsidian- ites :- "I was told by the native I had it from that it was taken out of the breast   of a sick man by one of their 'koonkies,' or   doctors, who, however did not succeed in saving the patient's life, as some other     'koonkie' of another tribe had a greater power than this one who took the stone out.   The sick native, I may mention died here   of disease of the lung, and all the 'koonkies' in the country could never have saved  

him."

Seeing there are no exrtra- terrestrial rocks in any way resembling obsidianites, either in form or composition, the meteoritic theory his no inferential foundition. Nor is the volcimc theory satisfacton, although forms of the shape of obsidianites can be easily conceived to be formed in the crater of a volcano. The chief objection is that there are no volcanic vents in the vicinity in which these bodies are found producing acid or siliceous rocks agreeing with the analysis of obsidianites with their 64 to 74 per cent. of silica. The strongest evi-

dence of their source and formation can be gathered from a comparison of the molda- vites or bottle-stones, of Moravia, re- sembling the Darwin glass of Tasmania and the glass balls of Billiton in the Malay States. The general term bottle-stone is applied to the fulgurites or lightning tubes, where the lightning penetrated sand or to fused splinters of rock, and the structure of obsidianites, with their streaky, fluidal  

structure and occasional bubbles, closely resemble these fulgurites.  

Is it not feasible. therefore to suppose  

that lightning was responsible for the for- mation of these buttons? This idea has long been held by the writer, and has also lately been suggested by E. J. Alexander in a recent column of "The Argus" (September 20). The dust rained down during a storm has often the composition of the obsidian- ites, especially that giving rise to "red rain." This dust from the interior of Australia,   caught up in a willy-willy and fused by   lightning, might easily result in these clearly   rotated bodies. the splitting off of rings and peripheral flakes being induced by their falling into streams.

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