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On a TERTIARY FORMATION at NEW GUINEA.
by Rev. J. E. TENISON-WOODS, F.G.S., and Corr. Mem. Linn. Soc.
During the voyage of the Chevert a tertiary formation was found at Yule Island, New Guinea, and the fossils brought home on the occasion have been submitted to my examination by Mr.
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W. Macleay. The rock is an extremely friable fine grained yellow limestone, very much like the limestone beds on the River Murray, in South Australia, but less consistent, as it powders by handling. Unlike the Murray limestones, or any of the Tertiary formations of Southern Australia, there seems to be a total absence of Polyzoa, neither could I detect any Foraminifera on subjecting different portions to microscopic examination. It seems to me to be rock which is derived from the detritus of a coral reef, and formed into a finely levigated limestone paste, stained yellow probably from the proximity of some ferruginous rocks. But there are no traces of coral, which is the more to be regretted, as from no organisms would the position of these beds be so easily determined, and their relation to other Australian Tertiary rocks, as from coral. Situated as the deposit is so near the tropics, the absence of any signs of corals is a matter of wonder. The shells are not numerous, and for the most parts mere casts. Pectens are however well preserved, and this is the case with the same genus in similar tertiary rocks at Mount Gambier. I propose to treat of the Mollusca in another paper. At present I intend to deal with the Echini, which are also well preserved. There were three detached specimens among the loose dust; two of one species and one of another, which I will now describe.
The first was Peronella decagonalis, Lesson. This species is a living form which is very wide in its distribution, being found in China, in the Indian Ocean, the Philippines, and in Australia. The Australian specimens are generally tropical, but it is not uncommon at Port Jackson and New Caledonia. The specimens, two in number, are extremely thin and concave on the actinal side, but they are both young specimens, and one scarcely above an inch in diameter.
TEMNECHINUS MACLEAYANA, sp. nov. I name this fossil provisionally, because it comes nearer to the genus described by Professor Duncan (T. lineatus) from Mordialloc, Victoria, than any other form known to me. But the abactinal area is encrusted, and cannot be made out. The test is small, depressed, circular,
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and the ambitus rounded. The actinal surface is slightly rounded and depressed to the actinostome. The interambulacral areas are twice the width of the ambulacra at the ambitus, and about one-third broader at the mouth. They are slightly depressed in the middle by an undulating line of suture which becomes a very distinct depression on the abactinal surface, on which the lines of the plates are well marked. The pores are in a vertical row, slightly oblique, and their zones sunken. The interambulacra have two rows of primary tubercles, each row being flanked again on each side by a vertical row of secondaries, all small imperforate, both primaries and secondaries surrounded by circles of granular tubercles, which are frequently connected with the main tubercle by a ridge. Ridges which are granular also separate the pores. The primaries of the ambulacra are in two vertical rows, each close to its poriferous zone. Their secondaries are not so visible, but the rings of granules are very manifest, with an indented vertical line of suture in the centre. Actinal opening large, with conspicuous but not deep indentations. Diam. 16, alt. 6 millimetres. The specimen had been slightly crushed by pressure so that the coronal plates were often disarticulated.
This genus is very well represented in the tertiary rocks of Great Britain, but principally I believe as a Pliocene form. D'Archiac and Haime have figured from the Nummulitic formation of India, a number of species which Agassiz (Revision of the Echini) regards as belonging to this genus, Temnechinus. One is found living in the American seas at a depth varying from 30 to 100 fathoms. The nearest affinities are T. globosus, of the British Crag.
From the evidence afforded by these fossils, and from a cursory examination of the mollusca, I should not be inclined to regard those beds as so old as those of the Murray River, Mount Gambier, or Cape Otway. If we consider the Mount Gambier beds as middle miocene, though there are strong reasons for placing them even lower in the series, we may look upon the Yule Island formation, from which these fossils were taken, as Lower Pliocene. It is a most interesting fact to find evidence of recent
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upheaval in New Guinea, especially as there has never been any similar evidence found on the east side of the Australian continent. It remains to be seen whether, in this case as in the Southern Australian tertiaries, we have the sign of volcanic activity accompanying the upheaval. Mr. Mackay showed me specimens of true amygdaloidal and vesicular dolerites, taken from the coast of Darnley Island, opposite Yule Island, a distance however of 150 miles. They were in all respects similar to the Victorian pliocene dolerites. The bathymetrical evidence of these fossils show that at least there has been upheaval to the extent of 400 or 500 feet.