45 4 The National Geographic Magazine 



jected to the action of a powerful sand- 

 blast. The ordinary erosive action now 

 is that the heavy rains take up vast 

 quantities of the loose lapilli for use 

 as . a powerful scouring agent in at- 

 tacking the denuded hillsides, and thus 

 old valleys are being deepened and 

 widened. 



The particular feature of the May 

 eruptions of La Soufriere was the enor- 

 mous amount of dust which was thrown 

 into the air and distributed over a vast, 

 somewhat elliptical area, the extent of 

 which cannot yet be calculated for lack 

 of data. The British steamship Coy a 

 had an eighth of an inch of volcanic 

 dust from this volcano fall on her deck 

 when she was 275 miles east-southeast of 

 St Vincent. The steamer encountered 

 the dust at 10.30 p. m., May 7, 8}4 

 hours after the eruption of La Sou- 

 friere began, indicating transport 

 against the prevailing surface wind 

 at more than thirty-two knots per 

 hour. Reports of vessels from the 

 west (leeward) of the island have 

 not come to my notice, but the state- 

 ments of the islanders would indicate 

 that the greater proportion of the cloud 

 of dust went to the east and southeast. 

 The dust was spread like a gray mantle 

 over the island, generally diminishing 

 in thickness from the crater outward, 

 but collected in vast deposits in certain 

 valleys on the sides of the mountain, 

 where the conditions seem to have been 

 particularly favorable. The chief of 

 these beds were formed in the Wallibu, 

 Trespe, and Rozeau valleys, on the lee- 

 ward (west) side, and in the valleys of 

 the Rabaka Dry River and its tributaries, 

 011 the windward (east) slope, with by 

 far the greatest thickness along the 

 Wallibu and Rabaka Dry rivers. In 

 the valley of the Wallibu the deposits 

 were not less than sixty feet deep in 

 places, while in the Rabaka Dry River 

 the fresh material filled a gorge which 

 is said to have been two hundred feet 

 deep before the eruptions began. From 



a distance this deposit looks as if it were 

 a glacier coming out of the mountains. 



The dust began to fall upon the 

 Island of Barbados about 5 p. m., in- 

 dicating the same rate of transport. 



Several other reports quoted in the 

 West Indian Bulletin, vol. iii, No. 3, p. 

 282, agree fairly well with this esti- 

 mated rate of transport. One report 

 reads: " May 8, hark. Jupiter from Cape 

 Town met dust at 2.30 a. m., 830 miles 

 E. S. E. of Barbados," which would 

 give a speed of 60 miles per hour. This 

 great rate is so far in excess of what is 

 indicated by the reports of the other 

 ships that discredit is cast upon the 

 report. 



The following chemical analysis is of 

 dust which I collected May 27 in a room 

 in the Langley Park estate house, about 

 one mile north of Georgetown, in which 

 21 dead bodies were found after the 

 eruption of May 7. The analysis was 

 made by Dr W. F. Hillebrand, of the 

 United States Geological Survey, to 

 whom m} r acknowledgments are due, 

 and is the unpublished analysis referred 

 to in his article in the July number of 

 this Magazine (vol. xiii, p. 297) as 

 emphasizing the greater amount of sul- 

 phur present in the ejecta of La Soufriere 

 than in those of Mont Pelee. The ab- 

 sence of chlorine is interesting as indi- 

 cating fresh waters as the probable 

 source of the steam of the eruptions, 

 in spite of the close proximity of the 

 ocean : 



SiO. 5508 



Al.,6 ;i 1S.00 



Fe,0 3 2.46* 



Feb 4-57* 



MgO 3-34 



CaO 7.74 



Na„ O 3 45 



K,6 0.65 



H.,0 at ioo° C 0.66 



H.^O above ioo° C 1.39 



Tib, 0.S0 



ZrCX (?) 



C0 2 None 



*Ouly approximate, because of effect of 

 pyrrhotite, 0.91 per cent. See below. 



