948 



SCIENCE. 



[N. S. Vol. XV. No. 38'J. 



to mark zones of crystal growth. Quartz and 

 orthoclase may be present in small quan- 

 tities but they could not be positively deter- 

 mined. 



Apparently two forms of pyroxene are pres- 

 ent, a pale green non-pleocbroic form whose 

 prismatic fragments extinguish at a large 

 angle and is probably augite, and a pleochroic 

 yellowish form like hypersthene, but ap- 

 parently having inclined extinction. 



The glass particles vary greatly. Many are 

 perfectly clear and transparent but rarely 

 show the concave boundaries which are com- 

 monly characteristic of glossy volcanic dust. 

 Occasional clear fragments are filled with 

 microlites, minute crystals whose development 

 was arrested by the eruption. 



Opaque, white or yellowish-gray pumiceous 

 fragments full of gas cavities are common and 

 give color to the mass of which they constitute 

 nearly twenty-five per cent. They appear to 

 represent the molten material which floated 

 the crystals and contained the explosive energy 

 of eruption, blowing the mass to sand and dust 

 with the relief of pressure. Although it is 

 possible that the dust came from several 

 sources, there is as yet no certain means of 

 distinguishing the material from the different 

 sources, nor in fact is there in the dust itself 

 a definite suggestion of more than one source. 

 In the process of crystallization the occluded 

 gases are in large measure rejected and con- 

 centrated in the amorphous portion of the 

 mass, so that when an outbreak occurs the 

 glassy parts record the greatest expansion. 

 The great distance traveled makes it probable 

 that the proportion of amorphous material 

 here is greater than in the original magma, for 

 the crystal fragments being heavier would 

 drop more readily than those of glass. 



The destruction of St. Pierre has been at- 

 tribiited largely to gases shot out from the 

 volcanic vent with burning sulphur, and it is 

 probable that the gases ejected by la Souf- 

 friere on St. Vincent were of a similar nature. 

 To get evidence concerning them it was pro- 

 posed to crush the fragments of pumice in a 

 vacuum and liberate the enclosed gases for 

 chemical investigation, but the amount and 



character of the material at hand was en- 

 tirely inadequate. 



An inquiry as to the presence of soluble 

 salts in the dust gave more definite data. 

 None of the dust components thus far enu- 

 merated are soluble in water nor has it a de- 

 cided taste, and yet when 10 grannnes of the 

 dust were treated with 400 cubic centimeters 

 of water for 2 hours on water bath a neutral 

 solution having the composition noted below 

 with proportions indicating that the sub- 

 stances dissolved were CaSo^ and NaCl and 

 constituted about .5% of the dust. They 

 were not discerned with certainty under the 

 microscope but are supposed to appear as 

 coatings deposited on some of the grains dur- 

 ing the eruption. The large amount of super- 

 heated water vapor usually given off by vol- 

 canic eruptions is generally accompanied by 

 much hydrochloric (HCl) and sulphurous 

 acids (So,), sulphurated hydrogen (H^S) 

 and other gases. The sulphurous acid upon 

 reaching the air partially oxidizes to sulphuric 

 acid, and with the hydrochloric acid would 

 naturally attack the shattered lime-soda 

 feldspar fragments forming a coating film of 

 gypsum and common salt. 



CHEMICAL ANALYSIS OF DUST FROM THE OOYA 



I. AND OF HYPERSTHENE ANDESITE II. FROM 



CRATER LAKE, OREGON. 



I. II. 



