Fossil Insect Wing in Gypsum
from Mount Elliot Mine,
NW Queensland

By Tony Forsyth

In the past I have published bits and pieces gleaned from the pages of old geo reports that I come across from time to time. They can make fascinating reading, especially the older ones that skip the scientific prose and can read like your average fossicking trip! A couple of years ago I was forwarded a piece for publication that was written by Corbould, the Manager of the mines, which described the crystal caverns to be found in the Mount Elliot mine in Northwest Queensland. This fabulous place is famous for its huge gypsum 'selenite' crystals that were metres long, transparent and criss-crossing cavities. Many crystals had bright native copper dendrites clearly visible throughout them. A number of these specimens are preserved in the Queensland Museum collection, although not on public display, from when the Qld Geological Survey collections were transferred to the Qld Museum. The pieces were collected around 1910-1915. Also mentioned in Corbould's book was the story of a dragonfly wing found preserved in one of these selinites. The specimen resides in the Australian Museum.

Recently I was browsing some old issues of the NSW Geological survey records and came across an article about this very subject, and interesting it is! The following article is an extract:

Records of the Geological Survey of New South Wales
Volume X, Part II, 1922

V.—An insect wing in a Crystal of Selenite (Order Orthoptera) ; by R. J. TILLYARD, M.A., Sc.D. and &c., Nelson, N.Z.
(Plate XV and text-figure)

" The fragment of an insect’s wing, which forms the subject of this paper, was discovered in 19... in the Mount Elliott Copper Mine, North Queensland. It was found at a depth of 260 feet below the surface-, embedded in a large crystal of selenite enclosed in the actual copper lode worked by this mine. It is, therefore,, the only fossil insect wing ever actually found in a mineral lode.

The lode in which the fossil was found is almost vertical, and outcrops through slate country. At the point where the fossil was found the lode is 120 feet wide, the position of the fossil itself being about eighteen feet from the footwall, which is here almost vertical. The actual crystal of selenite in which the fossil occurs is a beautiful specimen, very clear, but tinged with green and brown ores of copper, on the slant faces, and also on the edge closest to the fossil. Thickness of crystal, 20 mm. Upper surface a rhombus (approximately) on a side of 75 mm. ; angle 65'. Under surface roughly a parallelogram, sides 40 mm. and 85 mm. ; angle 65'. The fossil lies embedded about 2 mm. below the upper surface of the crystal.
The fossil wing of Austrodictya corbouldi, n.sp., in situ in crystal of selenite. (for size compare shilling in photograph) and magnified

This fine specimen was forwarded by Mr. Corbould, Qld., manager of the Mount Elliott mine, to the Geological Survey Branch, Department of Mines, Sydney New South Wales, and is now in their Museum. 1 desire to thank Mr. W. S. Dun of this Department for his kindness in giving me the opportunity of studying this fossil, and I also thank him and Mr. Corbould for so readily supplying me with information about it.

It would seem that the most probable explanation of the occurrence of this wing-fragment in so remarkable a position is as follows: -

At the time of the formation of the copper lode, or shortly afterwards, large vugh channels must have existed, reaching to the surface of the outcrop. Down these, water percolated; and the wing, quite probably in its present fragmentary condition, as part of the remains of some dead insect, was either blown or washed into one of these channels, and carried downwards until it reached a resting place in some out-of-the-way corner. Here it became incorporated in some manner between the layers of crystallising selenite that have been found in several parts of the mine embedded in the lode material.

Under these circumstances, it is of course impossible to assign the fossil to any definite geological epoch. All we can say is that the lode is older than the fossil, since the vugh channels must have been formed either by the cooling of the lode or by percolating waters. Also, these channels may have remained open for centuries, and the deposition of the gypsum crystals by minerally charged waters dripping from above may in itself have been the slow work of many years. Even though the lode itself might date back to the Paleozoic era, the age at which the deposition of the gypsum crystals took place, might still be only Tertiary. In order then to arrive at some definite conclusion on this matter, we can only fall back upon the evidence afforded by the fossil itself; and this, as we shall see, is fairly definite.

The conclusion which I have reached after a very careful study of the fossil is that it is an archaic type belonging to the family of Long-horned Grasshoppers (Tettigoniidee or Phasgonuridae, formerly called Locustidee), and that it does not belong to any genus known to exist in the world to-day. Mr. A. N. Caudell, the well-known Orthopterist of the United States National Museum at Washington, to whom I submitted a drawing of the fossil for expert opinion, has replied that ‘among recent genera, I know of nothing to which your insect can be referred.’ A careful study of known fossil Orthoptera indicates that, this wing is more highly specialized than any known Mesozoic type. This indicates that the fossil should be considered of Tertiary age, and preferably somewhat late Tertiary, in so far as it appears to be more closely allied to recent Long-horned Grasshoppers of the subfamilies Phasgonurinae and Conocephalinae than to anything known amongst fossils.

It is very unfortunate, from the point of view of paleontology, that so little use of the wing-venation has been made in the classification of the Orthoptera. The origin and relationships of the different venational types within the order are at present little understood. While excellent figures of the parts of the body used in classification are to he found in hundreds, yet very few reliable figures of the venation can be found, even in such standard works as the ‘Genera Insectorum.’ The comparison of the venation of the fossil had, therefore, to be made with such Australian, New Zealand, European, and American material as has been available to me. Fortunately, this includes a large number of types ; but I have not been able to find anything at all closely approaching the venation of the fossil. I have, therefore, decided to erect a new genus for it, and to place it definitely within the family Tettigoniidae, possibly as the only known representative, of a Tertiary subfamily now extinct, but closely allied to the Phasgonurinae and Conocephalinae.

The new species is dedicated to Mr. Corbould, who may be regarded as its discoverer, in so far as it was through, his endeavours that the specimen was saved from destruction and sent to the Department of Mines in Sydney."

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