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XXX.—Observations on the Recent Calcareous Formations of the Solomon Group made during 1882–84

Published online by Cambridge University Press:  06 July 2012

H. B. Guppy
H. B. Guppy
Affiliation:
Surgeon H.M.S. “Lark.”
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Extract

On account of the treacherous character of the natives of the Solomon Group, no extensive geological observations have ever been made in these islands since the period of their discovery by the Spaniards three centuries ago. For this reason my excursions in these regions were not free from personal risks; in many places they were considerably curtailed, and in some places they had to be abandoned altogether. Fortunately, however, I was able to make a detailed examination of several of the smaller islands, the natives of which had been first conciliated by the kindly tact of Lieut.-Commander C. F. Oldham, to whom I am indebted for much assistance in my pursuits. But from the circumstances in which I was placed, both on board and on shore, it was necessary, in order to accomplish much, to dare a little.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 32 , Issue 3 , February 1886 , pp. 545 - 581
Copyright
Copyright © Royal Society of Edinburgh 1886

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References

page 546 note * In the examination of these calcareous rocks, as well as in the preparation of this paper, I have been assisted by Mr John Murray, to whom, as well as to the Abbé Renard, I have to express my indebtedness. I also desire to express my thanks to Mr Murray's assistants in the “Challenger” Office, Mr Fred Pearcey and Mr James Chumley.

page 546 note † For further information on this subject vide a paper on “The Nomenclature, Origin, and Distribution of Deep-Sea Deposits,” by John Murray and A. Renard, in the Proceedings of the Royal Society of Edinburgh, 1883–1884, pp. 504–506.

page 548 note * In a limited locality in the south part of the island the rock was a very fine grained calcareous tuffa, containing a few siliceous marine organisms.

page 550 note * Very frequently corals play only a secondary part in the building up of the rock which is largely composed of calcareous Algæ, fragments of Echinoderms and Molluscan shells.

page 551 note * I paid especial attention to the position of the imbedded corals, and only found two inverted. The large shells of Tridacna gigas are also enclosed in the rock in the usual position occupied during the life of the mollusc.

page 551 note † The general dip would appear to be away from the elevated interior of the island.

page 553 note * At the foot of these cliffs a rich red ochre-clay has accumulated, probably as washings from the cliffs above. It contains only 15 to 20 per cent, of mineral particles, and exhibits but a very slight effervescence with dilute acid.

page 555 note * Augite-andesite and porphyritic felsite, &c.

page 558 note * A small patch of massive coral, which still adheres to its surface, probably found attachment during the most recent upheaval of the island (vide posted).

page 558 note † This slippery slope, which is of the argillaceous rock to be immediately referred to, is in part encrusted by calcareous tufa, containing, at au elevation of 15 feet above the sea, a few small angular fragments of volcanic rocks. These fragments would appear to indicate the vicinity of the parent mass further in from the reef-flat.

page 563 note * I found a similar chalk-like coral rock in the small island of Bin which lies off the north end of Ugi Island. This island is only 1½ miles in length and about a hundred feet in height in its centre where this rock was found. It may be briefly described as a patch of coral reef which has been elevated about a hundred feet. In the southern island of the Three Sisters, which are adjacent to Biu, I obtained from the elevated central portion hand-specimens of coral rock which were in part chalky. This island, like Biu, is simply a patch of coral reef which has been upheaved 60 or 70 feet above the sea. The present reefs which skirt the more elevated portion have a rude atoll form.

page 564 note * Dr Leonard Dobbin, who determined for Mr Murray the carbonate of lime in the rock samples, writes :—“I would draw your attention to the result obtained in the case of the sample “Shortland Island, No. 587,” where the usual calculation, from the observed weight of carbonic acid, seems to indicate an almost theoretical composition of calcium carbonate. As our method could not give such a result with pure calcium carbonate (the results being in every case at least 2 per cent, too low), I tried to find out the cause of this rather anomalous result. The first and most likely explanation was that the specimen contained considerable quantities of magnesium carbonate, and I find that is the correct explanation, as I found on examining it that a good deal of magnesia is present. I may add that the carbonic acid is not liberated from this specimen with anything like the rapidity with which it is liberated from the other specimens.”

page 565 note * The appearance of this solitary specimen of Rhynconella Grayii, which is contained in the British Museum collection, might suggest its having been washed out of some recent deposit. I am informed, however, by Mr Davidson that portions of the mantle, peduncle, and some muscular fibres were still attached to the shell.

page 567 note * This grained limestone has not been examined by Mr Murray. It, however, closely resembles in appearance the Foraminiferal limestones of Alu, and is probably of the same character.

page 570 note * This estimate refers only to the coast. In the elevated interiors of the larger islands the annual fall is probably twice as much; whilst on the lofty summits of Bongainville and Guadalcanar the rain-fall is still greater.

page 571 note * A similar rock, but sparingly Foraminiferous, occurs on the slopes of Cape Keibeck at an elevation of 500 feet above the sea.

page 574 note * In one of the islands of the Pelew Group, Professor Semper observed that the base of the coral cliffs was formed entirely of species of Lophoseris mixed with other deep-sea forms, the higher portion of the cliffs containing Astræidce, Poritidæ, Madreporidæ, &c. Lophoseris and Leptoseris belong to the same sub-family of the Fungidæ. See The Natural Conditions of Existence, &c., p. 275, London, 1881. I am inclined to consider this variety of rock in Treasury Island as representing the base of the elevated reef-masses, since it only occurs on the higher and more denuded slopes.

page 574 note † Some specimens of coral rock which I obtained at Santa Anna were entirely formed of the joints of a calcareous Alga, resembling apparently the genus Halimeda, which are found commonly in the soundings off the outer edge of the present coral reefs.

page 575 note * White men resident in the group tell me that chalk-like rocks are found in the island of Ulaua, which lies near the Three Sisters.

page 579 note * Principles of Geology, 12th edit., vol. ii. p. 612.