J. W. Shipley — Volcanic Emanations in Alaska. 151 



asli which because of its location on the peninsula axis 

 was largely composed of pre-eruptive material blown to 

 powder. 



Metamorphic action of the Volcanic Gases. — The coun- 

 try rock (volcanic ash and pumice) in the neighborhood 

 of an active vent was subjected to the chemical action of 

 permeating gases and solutions. The porous character 

 of the rock permitted easy, intimate, contact and also 

 offered the maximum of surface so that chemical action 

 was speedy and effective. Adjacent to the hot acid vents 

 the ash was completely disintegrated. As the distance 

 from the vents increased the metamorphism diminished 

 until the unaffected ash was reached. The decomposi- 

 tion resulted in the formation of more or less soluble 

 salts of the bases present in the ash combined with the 

 acids free in the volcanic vapors or dissolved in the per- 

 colating waters. These salts were deposited at or near 

 the surface on the evaporation of the water or within 

 the vent itself if the temperature was above the boiling 

 point of water. In the latter case the salts were anhy- 

 drous. 



Two partially metamorphosed samples of the volcanic 

 ash, after extraction- with water, were analyzed. The re- 

 sultsshow a loss of silica, sodium and potassium with a 

 relative concentration of the iron and alumina. These 

 samples were from areas where hydrofluoric acid was 

 present in the vapors and consequently the loss of the 

 Si0 2 would be expected, in fact, deposits of amorphous 

 Si0 2 occurred around the vents at the surface. 



Analysis of partially metamorphosed volcanic ash {percentages). 



Sample SiO,, AL0 3 , Fe 2 3 , MnO, CaO, MgO, Na 2 0, KoO, F 



I.— 50-6 21-1 14-8 0-3 5-0 4-8 3-4 0-8 1-0 



II.— 60 6 -21-6 5-7 — 5-5 5-9 — — 1-1 



Sample No. II was more decomposed than No. I having 

 lost much of its iron. 



Pneumatohydatogen.esis.-The above term was applied 

 by Bunsen to the combined action of gases and water solu- 

 tions m the formation of salts. The salts and compounds 

 found in the Valley of 10,000 Smokes have their origin in 

 such combined action. Hydatogenesis in the valley is 

 confined largely to the surface layers for, as already men- 

 tioned, the temperature of many fumaroles is above that 

 of the critical temperature of water and consequently, 



