468 Notices of Memoirs — Dr. Tempest Anderson — St. Vincent. 



X. — The Soufeiere of St. Vincent : The Changes subsequent to 

 THE Eruption of 1902.^ By Tempest Anderson, D.Sc, F.G.S. 



IN 1902 the author visited St. Vincent, along with Dr. Flett, after 

 the then recent eruption. In 1907 he revisited the island and 

 examined the changes that had taken place in the new deposits. 



In 1902 an incandescent avalanche descended into the valleys which 

 occupy the great transverse depression across the island to the south of 

 the Soufriere, and in particular the Wallibu Valley was filled for 

 a great part of its course to a depth of at least 100 feet, but less near 

 its mouth. In this deposit of red-hot material the secondary 

 phenomena of re-excavation of the valley by the river, the falls of 

 hot ash, the steam explosions, and the flows of boiling mud took 

 place, and are described in the Heport, Part I.- In 1907 almost the 

 whole of this ash had been washed away, but a fragment remained in 

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

 of the valley. The ash of which it is formed is unstratified, and 

 contains very 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 

 valley. "When examined in March, 1907, it ran along the south side 

 of the valley, and had already in those few months excavated a new 

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

 new valley, is very distinct, and the sorting 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 

 better preserved, so that traces of the feather-pattern erosion, so notice- 

 able 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 

 beds of recent material. 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 their beds two new valleys 

 are formed where only one previously existed, and the walls of each 

 are composed on the one side of the new ash and on the other of older 

 tuff, with occasional terraces.* 



An account was also given of a visit to Montagne Pelee, in. 



' Abstract of paper read at the British Association in Dublin before Section C 

 (Geology), September, 1908. 



2 Anderson & Flett, Phil. Trans., 1903, Series A, vol. 200; Anderson, 

 Geographical Journal, March, 1903. 



3 See, further, Anderson, Report, Part II, Phil. Trans., Series A, vol. 208, 

 pp. 275-300; Flett, Petrology, ibid., pp. 304-33. 



