256 



Note on a Volcanic Ash from the Island of 

 Tanna, Nkv/ Hebrides. 



By Prof. Rennie, M.A., D.Sc, and Mr. E. R Turner. 



[Read August 4, 1891.] 



The volcanic ash of which we give an analysis below was for- 

 warded to one of us by the Rev. W. Gray, missionary to the 

 Presbyterian Church of South Australia, in the island of Tanna. 

 The ash was collected at a distance of several miles from the 

 volcano. The following is an extract from Mr. Gray's letter on 

 the subject : — "The cone on the island of Tanna is about 600 feet 

 high. The crater basin, oval in shape, is about a mile in circum- 

 ference. It is about 200 feet deep, and contains several vents, 

 from which eruptions take place every three minutes or so. The 

 dust is thus thrown out, and carried for more than 20 miles. The 

 heavier stuff falls nearer the cone, the lighter farther away. But 

 the output of dust varies much in this respect. Sometimes there 

 is very little rough stuff in it ; sometimes it contains a large pro- 

 portion of clear white particles. The dust, when accompanied by 

 rain, destroys some kinds of vegetation. It makes water hard, 

 and curdles milk." Mr. Gray also states that the fine "hairs" 

 which it often contains are called Pele's Hair, Pele being the god- 

 dess who presides over a volcano in the Hawaiian Islands. 



With regard to the destruction of vegetation, the making 

 water hard, and curdling milk, there can be little doubt that 

 these effects are due, not to the ash, but to acid vapours emitted 

 by the volcano during eruption, and carried down with the rain, 

 especially as quantities of sulphur are known to exist in conjunc- 

 tion with the volcano. 



The following figures are the mean of those obtained in twa 

 closely-agreeing analyses : — 



Silica (SiO,) .... 



Alumina (Al^Og) 



Ferrous oxide (PeO) 



Ferric oxide (FCgOg) 



Manganese oxide (MnO) 



Lime(CaO) ... 



Magnesia (MgO) 



Potash (K,0) ... 



Soda (Na^O) ... 



Phosphorus pentoxide (P 



