550 



NA TURE 



[April 9, 1908 



during ihe author's second visit lie in (i) the changes 

 wrought by denudation on the deposits left by that erup- 

 tion ; (2) the light thrown by those changes on the opera- 

 tion of the forces which had moulded the features of this 

 island in its earlier history ; (3) the information he was 

 able to collect with regard to the volcanic disturbances 

 subsequent to the great eruption of May, 1902 ; and (4) 

 the return of vegetation to the devastated areas. 



In the 1902 eruption a certain amount of the ejccta 

 overtopped the Somma ring, i.e. the remains of the 

 original great crater, and descended some of the valleys to 

 the north of it ; but by far the greater portion was dis- 

 charged into the transverse depression which extends right 

 across the island and separates the Soufri^re from the 

 mountain known as Morne Garu, about three miles to the 

 south. The water from the crater lake was discharged 

 at the beginning of the eruption down the Rabaka and 

 Waliibu rivers, while the solid and gaseous ejecta, in the 

 form of the incandescent avalanches and black clouds, 

 descended to both sides of the island. 



The most important geological phenomena were observed 

 in the Waliibu district. These phenomena have been fully 

 described in the published report, as also the subsidence 

 of part of the coast. To this district, therefore, attention 

 was especially directed in 1907 with the view of observing 

 the further progress of the changes and the return of 

 vegetation. 



A description of the Waliibu valley is given in the full 

 paper. In that district the beds of newer date have been 

 dissected into flat-topped plateaux by small rivers running 

 m deep gorges, which have again" been filled in places 

 by ejecta of eruptions and re-excavated in different degrees, 

 and sometimes on different lines, leaving plateaux and 

 terraces of different ages and heights. This action is well 

 exemplified in the lower valley of the Waliibu. In the 

 1902 eruption this part of the valley was filled by the 

 mcandescent avalanche to a depth of at least 100 feet in 

 the upper part, and less towards the sea, and it was in 

 this deposit of hot ash that the explosions of steam and 

 hot ash, flows of boiling mud, and other secondary pheno- 

 mena took place. In 1907 almost the whole of 'this ash 

 had been washed away, but a fragment remained in the 

 shape of a terrace 60 feet to 80 feet high, situated on the 

 north side of the valley. The ash of which it is formed 

 IS unstratified, and contains verv few ejected blocks or 

 fragments of any kind. The floor of the valley is all 

 composed of water-sorted material, chiefly gravel and 

 coarse sand, but with a good many blocks as big as a 

 man's head. They represent ejected 'blocks and fragments 

 of lava derived partly from the ash of 1902 and partly 

 from older beds, the fine ash in each case having been 

 washed away. The surface of the gravel bed showed 

 marks of quite recent running water, and during the 

 last winter, 1906-7, the river ran along the foot of the 

 north bank of the vallev. When examined in March 

 1907, it ran along the south side of the vallev, and had 

 already in those few months excavated a new channel 

 about 30 feet in depth. The stratification, as exposed in 

 the side of this new valley, is very distinct, and the sort- 

 ing by water, mentioned above, is very evident. Further 

 up the mountain the remains of the avalanche became 

 more abundant in the valley bottoms, and here they were 

 also often better preserved, so that traces of the feather 

 pattern erosion, so noticeable in 1902, were still visible 

 on the surface. This was mainly due to the surface of 

 these ash deposits, like those to be presently mentioned 

 on the plateaux and on the ridges, having consolidated 

 into a crust almost like a cement pavement which resists 

 the action of the rain. 



Another interesting point was observed with regard to 

 these massive ash deposits. Instead of one stream re- 

 establishing itself along the centre of the deposit, the 

 tendency is for a new stream to form on each side at or 

 near the junction of the new ash with the old valley 

 slopes ; and, as these streams deepen themselves, two new 

 valleys are formed where only one previously existed, and 

 the wv-ills of each are composed on the one side of the 

 new ash and on the other of older tuff, with occasional 

 terraces of new^ ash. It appears to be due to the fact 

 that the water from the old slopes, in running down into 

 the original valley, meets the soft new ash, and at once | 

 NO. 2006. VOL. 77] 



turns down along the valley and so starts the new stream, 

 and it seems likely that the chief cause of its so turning 

 is that the surface of the deposit tends to be higher along 

 the middle of the valley than at the sides, as is usual 

 with mud-streams or glaciers. A good example of the 

 action above described is to be found in a wide valley 

 to the north of and parallel with the lower Waliibu valley, 

 and bounded on the south by the Waliibu plateau. Before 

 the 1812 eruption the Waliibu river flowed down this 

 valley, but its course was changed after that eruption. 

 The floor of the valley is now occupied by the gorges of 

 two small rivers, divided by a very narrow ridge, formed 

 of ash different from and less consolidated than that com- 

 posing the walls of the main valley, and considerably 

 lower than the Waliibu plateau. In 1902 both these gorges 

 were filled with new ash to the level of the main valley 

 floor. One of these, the Tresp^ gorge, now emptied of 

 the 1902 ash, shows its north wall to be much higher 

 than the south, and also formed of older and more con- 

 solidated tuff. The same conditions, with sides reversed, 

 are seen in the other gorge, the higher bank in that case 

 being the Waliibu plateau to the south. 



The Waliibu plateau is composed of ash older than that 

 dividing the above two small rivers, but still comparatively 

 new, and its fljjt top and precipitous sides, both north and 

 south, proclaim it to .be in an early stage of denudation, 

 while the south bank of the Waliibu river on the south 

 of the plateau is composed of older tuff and lava, and 

 shows a much more mature type of denudation, viz. sloping 

 hills with rounded or ridged tops, and a good deal 

 weathered into valleys or gullies. The north face of the 

 plateau, like the south, is precipitous, and obviously much 

 less advanced in weathering than the slopes of the 

 Soufrifere on the opposite side of the broad valley of 

 the Waliibu Dry, and Tresp^ rivers to its north. The 

 mass appears to be the remains of an avalanche, or 

 succession of avalanches, of hot ash poured into the de- 

 pression between the Soufrifere and Morne Garu, on an 

 enormously larger scale than anything formed by recent 

 eruptions. It may be that the present bed of the Waliibu 

 to the south and the broad valley to the north are enlarged 

 and deeply excavated developments of the valleys that 

 were formed at the sides of this prehistoric avalanche. 



Descriptions of the changes in the fans and low 

 plateaux subsequent to 1902, of the shore subsidence, and 

 of the upper slopes of the mountain, are given in the full 

 report, as well as a detailed description of the crater as 

 seen in 1907. 



The topography of the old crater is still correctly re- 

 presented on the Admiralty Chart (published with the 

 report, part i.). The whole of the interior of the crater 

 is still quite bare, without any trace of returning vegeta- 

 tion ; small patches of moss appear about the rim and 

 on the slopes outside, then grasses, herbaceaus plants, 

 and large sheets of ferns, and lastly, below a height of 

 about 1500 feet, luxuriant tropical vegetation. It is 

 interesting that this sequence presents many points of 

 resemblance with that observed on Krakatoa. 



The present condition of the devastated areas is de- 

 scribed fully in the report, which contains also a history 

 of subsidiary eruptions which followed the great one of 

 May, 1902. The difference in character between the erup- 

 tions of the Soufri^re and Montagne Pel^e, referred to in 

 the report of 1902, appears to have continued since that 

 year, the outbursts from the former volcano being 

 generally less frequent but more violent than from the 

 latter. 



The report also contains an account of a subsequent 

 visit to the volcano of Montagne Pel^e, in Martinique, with 

 a description of the crater as the author then found it ; a 

 discussion of the phenomena of the remarkable extrusion 

 and subsequent destruction of the dome and spine, which 

 have been described by Lacroix and others, and a com- 

 parison of the soquelas of the great eruptions in the two 

 islands of Martinique and St. Vincent. 



Entomological Society, March 18 — Mr. C. O. Waterhouse, 

 president, in the chair. — Exhibits. — Dr. T. A. Chapman : 

 Photographs of the empty egg-shells and young larvae of 

 Pnpilio homcnis. — G. C. Gahan : (i) .■\ remarkable larva 

 of the Trictenomida", which, though heteromerous, was 

 wliollv different in character to the larvEC of that group; 



