Читать книгу The Solomon Islands and Their Natives - H. B. Guppy - Страница 4

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The Solomon Islands cover an area 600 miles in length. They include seven or eight large mountainous islands attaining an extreme height, as in the case of Guadalcanar and Bougainville, of from 8,000 to 10,000 feet, and possessing a length varying from 70 to 100 miles, and a breadth varying between 20 and 30 miles. In addition, there are a great number of smaller islands which range in size from those 15 to 20 miles in length to the tiny coral island only half a mile across. The islands fall naturally into two divisions, those mainly or entirely of volcanic formations and those mainly or entirely of recent calcareous formations.

In the first division, St. Christoval may be taken as a type of the large mountainous islands possessing massive profiles, such as Guadalcanar, Malaita, Isabel, etc. St. Christoval, which rises to a height of 4,100 feet above the sea, is composed in the mass of much altered and sometimes highly crystalline volcanic rocks (such as, in their order of frequency, dolerites, diabases, diorites, gabbros, serpentines, and saussuritic felspar-rock) which, as I learn from Mr. T. Davies, have been both formed and altered at considerable depths and indicate great geological age and extensive denudation. Recent calcareous rocks, such as will be subsequently referred to in the description of the second division of islands, flank the lower slopes at the sea-border up to an elevation of 500 feet. Fragments of similar diorites, dolerites, and other dense basic rocks, all much altered and often schistose, have been transported by trees to the coral islets off the coasts of Guadalcanar and afford evidence of the geological structure of that island. Serpentines were obtained by Dr. Hombron in 1838[1] from St. George’s Island, which is “ipso facto” a portion of Isabel. Bougainville and New Georgia are largely of more recent origin, as is indicated by their numerous symmetrical volcanic cones. However, the geological evidence at present at our disposal points generally to the great antiquity of the larger islands. The significance of this fact will be subsequently referred to. There can be little doubt that some of the mountainous islands will be found to yield in quantity the ores of tin and copper. A resident trader, Captain John Macdonald, has discovered arsenical pyrites and stream tin at the head of the Keibeck River in the interior of St. Christoval. A sample of stream tin from the south-east part of Bougainville was given to me by the Shortland chief. Copper will not improbably be found in association with the serpentine rocks of these islands.

[1] “Voyage au Pole Sud et dans L’Océanie,” (D’Urville). Géologie: part ii., p. 211.

The smaller islands of volcanic formation group themselves into two classes:

(1.) Those which, like Fauro and some of the Florida Islands, are composed partly of modern rocks, such as hornblende and augite-andesites with their tuffs and agglomerates, and partly of ancient and often highly crystalline rocks such as, as I am informed by Prof. Judd and Mr. T. Davies, quartz-diorites, quartz-porphyries, altered dacites and dolerites, serpentines, saussuritic felspar-rock, etc.

(2.) Those that are composed entirely or in the main of recently erupted rocks, islands which preserve the volcanic profile, possess craters, and sometimes exhibit signs of latent activity. Eddystone Island, which I examined, is probably typical of the majority of the islands of this class, such as Savo, Murray Island, and many others. It is composed of andesitic lavas of the augite type, is pierced by many fumaroles, and has a crater in the solfatara stage. Savo, though quiescent in the present day, has been in eruption within the memory of living men, and was in a state of activity in 1567 when the Spaniards discovered the group. Fumaroles and sulphur-deposits occur in Vella-la-vella. It may, however, be generally stated that the volcanic forces in these regions are in a quiescent condition at the present day, there being only one vent in active eruption, viz., Mount Bagana in the interior of Bougainville. Many small islands with volcanic profiles show no evidence of a latent activity. Amongst them I may mention those of Bougainville Strait, which are composed of andesitic lavas of the hornblende type.

I now pass to those islands which are composed mainly or entirely of recent calcareous formations.[2] Excluding the innumerable islets that have been formed on the coral reefs at the present sea-level, we come first to those small islands and islets less than 100 feet in height, such as the Three Sisters and Stirling Island, which are composed entirely of coral limestone. In the next place there are islands of larger size and greater height, such as Ugi, which are composed in bulk of partially consolidated bedded deposits containing numerous foraminifera, and possessing the characters of the muds which were found by the “Challenger” Expedition to be at present forming around oceanic volcanic islands in depths probably of from 150 to 500 fathoms. Coral limestones encrust the lower slopes of these islands and do not attain a greater thickness than 150 feet. The next type is to be found in Treasury Island which has a similar structure to that of Ugi, but possesses in its centre an ancient volcanic peak that was once submerged and is now covered over by these recent deposits. Then, there are islands, such as the principal island of the Shortlands, in which the volcanic mass has become an eccentric nucleus, from which line after line of barrier-reef has been advanced based on the soft deposits. These soft deposits contain amongst other organic remains, the shells of pteropods and the tests of foraminifera in great abundance. In such islands I did not find that the coral limestone had a thickness of as much as 100 feet. In this island the upraised reefs are based upon hard foraminiferal limestones. Lastly, we have the upraised atoll of Santa Anna which within the small compass of a height of 470 feet displays the several stages of its growth; first, the originally submerged volcanic peak; then, the investing soft deposit resembling in character a deep-sea clay and considered to have been formed in considerable depths, probably from 1500 to 2000 fathoms; and over all, the ring of coral limestone that cannot far exceed 150 feet in thickness. The islands formed mainly of the soft foraminiferous deposits have long level summits free from peaks. Judging from their profiles, the islands of Ulaua and Ronongo will be found to possess the structure of Ugi and Treasury. The western end of Choiseul has a very significant profile, and I have little doubt from my examination of the lower slopes that this extremity of the island is mainly composed of the recent soft deposits.

[2] Vide my paper on this subject (Trans. Roy. Soc. Edin.: vol. xxxii., p. 545), and my work on the geology of this group.

I now proceed to refer very shortly to the coral reefs[3] of these islands. The three principal classes are to be found in this region; but of these, the fringing and barrier-reefs are more commonly distributed, whilst the atolls are comparatively few in number and of small size. A line of barrier-reefs, probably not much under 60 miles in length and bearing innumerable islets on its surface, fronts the east coasts of the islands of New Georgia at a distance of from one to three miles from the shore. Extensive reefs of the same class, having a broad deep-water channel inside them, lie off the large island of Isabel and off the south-coast of Choiseul. Barrier-reefs, of smaller extent, also skirt the west end of Guadalcanar and the southern end of Bougainville. I have referred particularly to these reefs because at the time that Mr. Darwin wrote his work on “Coral Reefs,” fringing-reefs were alone believed to exist in these islands.

[3] Vide my paper on this subject. (Proc. Roy. Soc., Edin., 1885–86.)

The larger islands of the Solomon Group are often separated from each other by depths of several hundred fathoms. St. Christoval, for instance, is separated from the neighbouring islands of Guadalcanar and Malaita by straits in which casts of 200 fathoms fail to reach the bottom. On the other hand, the same 100 fathom line includes both Bougainville and Choiseul. Judging, however, from the soundings obtained by Lieut.-Commander Oldham between the islands lying off the north coast of St. Christoval, it would appear probable that depths of 400 fathoms commonly occur between the islands of the Solomon Group. Although the soundings hitherto made in this portion of the Western Pacific go to show that this archipelago, together with New Ireland and New Britain, are included within the same 1,000 fathom line, which extends as a loop from the adjacent borders of New Guinea, we can scarcely urge this fact as evidence of a former land connection, seeing that one of the most interesting features in the geological history of this region is that of the enormous elevation which these islands have experienced in recent and probably sub-recent times. Independently of the character of the deposits discovered by me in the Solomon Islands, I arrived at the conclusion that there had been a recent upheaval of at least 1,500 feet. The characters of some of the deposits, as examined by Dr. Murray in the light of the “Challenger” soundings, however, afford indications of an upheaval of a far more extensive nature. I am informed, in fact, by Mr. H. B. Brady, that the foraminifera of some of the Treasury Island rocks indicate depths of probably from 1500 to 2000 fathoms. Geologists may look forward with the greatest interest to the results of the examination by Mr. Brady of the foraminiferous deposits of the Western Pacific. One of the most important results will be to establish the great elevation which has occurred in this region during Post-Tertiary times. We are therefore justified in regarding the island groups of the Western Pacific as having always retained their insular condition, situated, as they are, in a region of upheaval, and separated, as they are, from each other and from the Australian continent by depths of from 1,000 to 2,400 fathoms. I have already pointed out that the volcanic rocks of the large islands of the Solomon Group are geologically ancient. Their elevation and the great subaerial denudation which they have experienced afford indications of the insular condition having been preserved from remote ages. It is this prolonged isolation that explains the occurrence of the peculiar forms of the amphibia which I discovered in Bougainville Straits, and that accounts for many of the peculiarities of the fauna of this archipelago.

Having thus briefly considered the leading geological and hydrological features of this group, I pass on to consider these islands in the point of view of an intending settler. They are for the most part clothed with dense forest and rank undergrowth, and it is only here and there, as in the western portion of Guadalcanar and in limited localities in St. Christoval, that the forest gives place to long grass and ferns, a change often corresponding with the passage from a clayey and calcareous to a dry porous and volcanic soil. As a rule, the calcareous districts of a large island possess a rich red argillaceous soil, often 5 or 6 feet in thickness, and in such localities the streams are large and numerous. In the districts of volcanic formation the soil is dry, friable, and porous, whilst the streams are few in number and of no great size. In the principal island of the Shortlands the difference in the character of the soil between the volcanic north-west part and the remaining calcareous portion is well exhibited. In the smaller islands the soil varies in character according to the formation, those of volcanic origin being singularly destitute of streams.

In chapter XVII. I have dwelt with some detail on the climate. The healthiest portion of the group would, as I think, be found in the eastern islands, and the healthiest part of each island would be that which is exposed to the blast of the south-east trade during a large portion of the year. The excessive annual rainfall, the humid atmosphere, together with the enervating season of the north-west monsoon, are amongst the chief evils of the climate. Malarious districts can be readily avoided by shunning the low-lying damp districts on the lee sides of islands. Dysentery is rare on account of the general purity of the water. But, if we believe native testimony, which I have found most reliable and which in this instance agrees with my own, the streams draining calcareous regions are least liable to suspicion. Should an intending settler ask me whether the climate is suitable for the European, I would reply that with proper precautions as to his habits and the selection of a site, the white-man can here preserve his health as well as in most other tropical islands in these latitudes.

I will conclude this introduction with some remarks on the vexed question of making annexations and forming protectorates in the Western Pacific. From the eagerness of our Australian colonies to control them and of France and Germany to possess them, the presumption arises that the islands in this region are worth holding. Yet, how surprising have been the changes within the last four years! When in 1882 I was in the Solomon Islands, British influence was recognised as paramount in New Guinea and throughout the Western Pacific. At the present time the British flag has been almost squeezed out of the Western Pacific. In April of this year (1886), the British and German Governments came to an arrangement by which the northern side of New Guinea together with New Britain, New Ireland, and the adjacent western half of the Solomon Group passed under the protection, or in other words into the practical possession, of Germany; whilst Great Britain by this arrangement was to consider the remaining islands of the Western Pacific and the south coast of New Guinea as her sphere of action. It is only in New Guinea that Great Britain has exercised her right. Amongst the remaining islands of the Western Pacific she has little scope either for acquiring territory or for establishing a protectorate. France possesses New Caledonia and in a geographical sense she can claim not only the Loyalty Islands but the New Hebrides Group. There only remains then for Great Britain the Santa Cruz Islands and the adjacent eastern half of the Solomon Group, in which, if she chooses, she can exercise her rights without dispute.

England’s wisest policy in the Western Pacific is to recognise the existing condition of things, and to deal with France as generously as she has dealt with Germany. Stifling my own patriotic regrets, I cannot but think that the presence of Germany in these regions will be fraught with great advantage to the world of science. When we recall our spasmodic efforts to explore New Guinea and the comparatively small results obtained, when we remember to how great an extent such attempts have been supported by private enterprise and how little they have been due to government or even to semi-official aid, we have reason to be glad that the exploration of these regions will be conducted with that thoroughness which can only be obtained when, as in the case of Germany, geographical enterprises become the business of the State.

THE SOLOMON ISLANDS.