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



The deposition of Si0 2 probably results from the 

 decomposition of SiF 4 in the volcanic gases by the action 

 of the water contained in the gases. Many of the fuma- 

 roles have temperatures, a few feet within the orifice, 

 above the critical temperature of water, 375°C. Decom- 

 position of the SiF 4 would only take place after the 

 issuing gases had cooled off sufficiently to permit the 

 formation of water. The decomposition of the silicates 

 constituting the mud flow is quite marked over practically 

 all areas of activity and, immediately surrounding the 

 more active vents, the ash and pumice have been com- 

 pletely disintegrated. According to Moissan 10 Si0 2 be- 

 gins to volatilize at about 1200° C while Day and Shep- 

 herd 11 found it to sublime readily at 1755° C. There is no 

 indication of temperatures approaching these in the 

 fumaroles of the valley. 



Boron. — Qualitative tests gave no indication of the 

 presence of borates in the incrustants of the valley. 



Gypsum and Apatite. — Nodular concretionary deposi- 

 tions of mixed crystals with well-developed pure crystals 

 of selenite, halite and alum attached to the main mass 

 were frequently found covering the orifices of active 

 areas. Next to the deposits of Si0 2 these nodular masses 

 were the most common type of incrustation. The nodu- 

 lar mass on analysis proved to contain calcium, fluorine, 

 chlorine, phosphate (P0 4 ) and sulphate — the latter two 

 acid radicals predominating. Over the hotter vents the 

 principal constituent of the nodular mass was anhydrite. 

 Apatite was not definitely identified but was presumably 

 the form of phosphate present because of the association 

 with chlorine and fluorine. Thin layers of Fe 2 3 were 

 observed buried in these nodular masses. 



Alum. — Potassium alum in lichen-like incrustations was 

 forming in all active areas in the valley. After a few 

 hours without rain the accumulations became very appar- 

 ent only to disappear, wherever exposed, as soon as the 

 rain began again. The less soluble sulphates and phos- 

 phates of calcium preserved a lichen-like structure on 

 which the crystals of alum reformed when weather condi- 

 tions permitted. A small pond fed by surface drainage 

 over the mud flow was so impregnated with alum as to 

 be altogether unfit for drinking. 



Iron. — Compounds of iron were omnipresent, the beau- 



10 Compt. Rend., vol. 138, p. 243, 1904. 

 n Science, N. S., vol. 23, p. 670, 1906. 



