J. W. Shipley — Volcanic Emanations in Alaska. 145 



samples of the volcanic gases had been pnmped. The 

 incrustants tested in the laboratory almost all reacted for 

 fluorine. The amount present as fluoride varied froma 

 fraction of a percent up to 1% and was most abundant in 

 incrustants around the more acid fumaroles. No specific 

 compound of fluorine was identified but calcium was 

 usually present in more than sufficient amount to combine 

 with it, 



Apart from the importance of HF in the gases as a 

 disintegrating agent the presence of fluorine was very 

 significant as to the origin of the gases. Clarke 7 states 

 that fluorine compounds "are especially characteristic of 

 the deep-seated or plutonic rocks where the gaseous ex- 

 halations have been retained under pressure, and are 

 commonly regarded as of pneumatolytic origin." 



Corundum. — Several of the incrustants after decompo- 

 sition with sodium carbonate left a residue of small 

 crystals which on examination proved to be corundum. 

 The presence of these crystals is rather interesting in 

 view of Hautefeuille's s synthesis of corundum by the 

 action of HF on alumina and by Bruhns 9 in the wet way 

 on heating NH 4 F with alumina to a temperature above 

 300°. The conditions under which Bruhns synthesized 

 corundum obtain naturally in the Valley of 10,000 

 Smokes. 



Silica. — The most characteristic deposit of the fuma- 

 role activity consists of amorphous silica. Many fuma- 

 roles have built up deposits of almost pure Si0 2 several 

 feet high choking up the vents and causing the gases to 

 force their way out through secondary orifices in the 

 accumulated, baked, mass. Sulphur was frequently as- 

 sociated with these deposits and all samples tested in the 

 laboratory showed the presence of fluorine. These de- 

 posits of Si0 2 although most marked around the hotter, 

 acid, vents nevertheless were common over the whole 

 valley. Three of the purest samples analyzed as follows : 



Analysis of Silica deposits. 



Sample No. 



SiO, 



Free S 



Fe 2 3 



Undetermined. 





% 



% 



% 



% 



I 



93-5 



34 



30 



01 



II 



95-8 



3-9 



0-2 



01 



III 



96-7 



31 



.... 



0-2 



7 Data of Geochemistry, page 336. 



s Ann. Chim. phys., vol. 4, p. 153, 1865. 



9 Neues Jahrb., Vol. 2, p. 62, 1884. 



