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THE

GEOLOGICAL MAGAZINE.

NEW SERIES. DECADE II. VOL. VI.

No. VIII.-AUGUST, 1879.

ORIGINAL ARTICLES.

I.-A CRUISE AMONG THE VOLCANOS OF THE KURILE ISLANDS.
By Professor JOHN MILNE, F.G.S.,

TH

Imperial College of Engineering, Yedo, Japan.

(PLATE IX.)

THE following notes upon the Kuriles were collected during an excursion which I made to these islands in the summer of 1878. Owing to a continuance of foggy weather, which I do not think would find its equal even in Newfoundland, the want of harbours, and the strong currents, although I was almost a month steaming amongst these islands, it was seldom that we could effect a landing. In consequence of this the bulk of the material embodied in the following notes was written from what I saw from the deck of our vessel. However, as I had good opportunities for seeing nearly every island in the group, and many of these from several points of view, the following notes may not be altogether without value. One advantage which was gained by viewing these islands from a distance was, that I was thereby better able to judge of the number, and the general form of the mountains they contained, and to roughly make comparisons of their relative heights, than I could have done had I been actually on the islands themselves.

In a few cases I endeavoured to estimate the heights by means of sextant observations. I also made many measurements of the slopes of the mountains which I saw; but as these were made with a small hand clinometer from the deck of a rolling ship, these measurements must only be regarded as rough approximations.

I have spoken of several of these volcanos as conical, but it must be understood that this, in many cases, only indicates a general form, the true form of the slopes being approximately logarithmic.

In the majority of cases the mountains and different portions of these islands are without names, and I have therefore had to describe them by their positions.

We finished our journey northwards at the southern extremity of Kamschatka, which is terminated with high black snow-capped peaks, looking as cold, cheerless, and uninviting as the most dreary part of Iceland.

Commencing from the north we first have Shumushi or Pervi Island. This is the most northern of the Kuriles, and it is separated from Kamschatka by the Kurile Straits, which are about eight miles wide. Towards the south it is separated from Paramushir by the

DECADE II.-VOL. VI.-NO. VIII.

22

On

Little Kurile Strait, about two miles wide. As compared with the other islands in this group, Shumushi is extremely flat. Looking at it as we approached the northern entrance of the Little Kurile Strait, it presented an undulating surface. Where the convexity of these undulations came down to the shore, they terminated in low perpendicular cliffs. In other places which marked the low sweeping valleys, the land rose gently upwards and backwards as it receded inland. It was opposite to the entrance of one of these valleys at a place called Myrup where we anchored. Here there were three wooden houses which had been built by the Russians, and quite a number (perhaps a score) of half-underground dwellings. landing we found that all these were deserted, and in many cases even difficult to find, owing to the growth of wormwood and wild grasses. The inhabitants of the island, who call themselves Kurilsky, are twenty-three in number. They chiefly live at a place called Seleno about four miles distant. In addition to their own language, they speak Russian very fluently, and also know something of the Aino language. For the last three or four years they have lived on fish, a few blay-berries and the various animals they could shoot. I mention these people as they appear to be the only inhabitants in the Kuriles north of Iterup. By going up the bed of a small stream which flows down the Myrup valley, and by travelling along the shore, I saw several exposures which showed beds of breccia overlying beds of volcanic rock. At a distance this breccia is generally of a whitish grey colour. Looking along the shore from Myrup northwards, you apparently see beds of grey breccia overlying beds of a black volcanic rock. On close inspection, however, the black rock is seen to be also a breccia, coarse in its lower portion, where it contains fragments of rocks, gradually becoming finer higher up, and finally merging into a grey tuff. The difference in colour seems to be greatly due to a difference in weathering and the action of the sea. Here and there standing up through this breccia are bands and masses of volcanic rock. One of the former of these, which has had the breccia worn away from its sides, stands up at right angles to the shore-line like a huge wall.

Its continuance towards Paramushir is marked by outliers which, by the action of the sea-waves, have gradually been cut off from it. At right angles to its length-that is, in a direction running from side to side-it is seen to have a columnar structure, which, whilst adding to its peculiar appearance, gives you some idea of the way in which

it cooled.

Up the valleys masses of a similar rock are also to be found. Upon the sloping sides of these valleys the breccia (which was friable) is thick, but it is thinner near the tops of the hills.

As we entered the straits, to see headland facing headland was very noticeable. If we imagined the curves of the volcanic ridges from Paramushir to be continued eastwards across the straits, it was clearly evident that in many cases they would make an unbroken line. When on Shumushi, by looking across the Straits at Paramushir,

it was observable that in many cases the undulations, and more especially the bluffs, of the land on one side correspond with those upon the other. These observations suggested the idea that in times not far remote these two islands have been continuous. At the time when the high volcanos of Paramushir were in full activity, they probably gave forth the materials which form the breccia. At first these materials were large and coarse, but as the intensity of the eruptions gradually decreased, the ejectamenta became finer and finer, as is indicated in the deposit of tuff overlying the coarser stones. From the absence of any appearance of stratification, I should be inclined to think that this action was a continuous one; at first violent and fierce, and finally, after the beds in Shumushi had accumulated to a thickness of a hundred feet or more, weak and feeble, puffing out fine dust and ashes, which fell and formed the tuff. This continuous action, of which we have here evidence, I may remark, is very different to the action which has been carried on by the volcanos further south in Yezo and Niphon, where we have stratified beds of varying thickness, showing that sometimes we had a violent eruption, and next a feeble one. Sometimes these rapidly succeeded each other, but at other times, as is indicated by an intermediate layer of soil, there were periods of repose. The outbursts of the Japanese volcanos have been spasmodic; whilst the outbreaks which covered Shumushi, which apparently came from the high volcanos of Paramushir, have probably been more regular in their action. When speaking of these volcanos under the headings of the several islands in which they occur, I will give other reasons for my belief that the building up of many of the Kurile mountains has been by a continuous action rather than by a series of spasmodic efforts.

Immediately after these eruptions we must imagine the Kurile Strait to have been bridged across by the lower part of a continuous volcanic curve. Subsequently, because the materials which formed this bridge were soft, the sea has gradually eaten itself a channel through it. This channel is not like the channels between the other islands, almost unfathomable, but shallow. The greatest depth being about thirteen fathoms. Whilst this was going on, subaerial actions have worn out the ridges on the volcanos and the slight hollows on Shimshis, which now form the valleys, shallowing the sea by the material derived from the land near their entrance.

At the southern entrance to the Little Kurile Straits are a number of small islands called Torishima (Bird Islands). These I did not see. Alaid Island.-This is a small island lying almost eleven miles off the north-west coast of Paramushir. Its general appearance is that of a solitary cone. From a rough observation made at a distance of almost six miles this appears to be over 3,000 feet in height. When I first saw it, we were steering N.N.E. between it and Paramushir. At this place we sounded with forty-five fathoms of line without finding bottom. At that time the base of Alaid was covered with clouds, but above these the top showed itself like a huge wedgeshaped cap. The edge of the wedge, which apparently was the

ruined rim of an old crater, formed the top ridge of the mountain. This ridge is on the W.S.W. side. As we continued on our course, the N.E. end of this ridge rose in a point, and was seen to be the highest portion of the island. Subsequently, when I again saw this mountain, I had an uninterrupted view from its summit to the base. On the S.W. side the slope near the top was 25°. Lower down this gradually decreased to 12°. From the E.S.E. this side of the mountain was seen to have a slope of 30°, and an almost perfectly symmetrical appearance. The measurement of 25° had been taken along the edge of some degraded ridge which at the time of observation formed a profile of the mountain. On the N.E. side the slope at the top was almost 23°, and lower down 23°, and near the base 13°. From all points of view the mountain exhibited a distinct and beautiful curve. Looking at the surface, this was exhibited as a sweeping hollow. And if we except a few deep furrows which had been cut by rain and weather, its contour was perfectly regular.

Round the base of the mountain there was a growth of scrub.

In many places the shore-line was seen to be bounded by low cliffs. At the S.W. end these terminate in a small abrupt peak. These cliffs have in places a stratified appearance, a few thin earthy beds being intercalated with beds of ashes. From the way in which any one of these beds is seen to be continued along the shore-line, and also upwards along the scarp of the furrows, it would seem that the structure of the outer portions of this mountain must be that of a series of skins, or superimpose more or less conically formed envelopes. Although I looked carefully over the S.E., S., and S.W. slopes of this mountain, nowhere did I see anything which looked like or indicated the presence of a stream of lava.

From the structure exhibited by this mountain, the apparent absence of lava streams, and its beautiful form, the slopes of which, so far as the eye could judge, were of logarithmic curvature, this mountain, like many others in the Kuriles, of which I have yet to speak, was in all probability built up by a more or less continuous action, and consequently exhibited that elegant form which is natural to any heap of loose materials. Since the last eruption materials have been washed down from higher to lower levels, the top being made a little steeper, and the base more horizontal. [Alterations near the summit, tending to increase the steepness, have probably taken place more rapidly than at lower levels, from the fact that degrading agencies like rain would, for many reasons, be more active at high levels than at low ones. It is also possible that horizontality, and even a quaquaversal internal dip, may have been provoked, as Mr. Mallet has suggested, by the weight of the cone pressing down at the centre and raising up the rim]. During these processes furrows were cut which hold perennial snows, and plants which fringe the base grew up from drifted seed.

Paramushir Island. This island may be classed among some of the largest islands in the group. It is about 60 miles in length, as measured from N.E. to S.W.; its breadth is about 14 miles. From what I saw of it on the N.E, N., and N.W. shores, it appears to be

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