634 abstracts: geology 



southwest end of Kenai Peninsula. A description of the deposit now 

 mined and a map showing its location are given in the bulletin. 



6. The results of studies of the strata and of the structure in the 

 Matanuska coal field, Alaska, made in 191 7, are reported. The paper 

 includes sections showing the character, relations, and thickness of the 

 beds of rock and coal at many localities, as well as a graphic section 

 showing a tentative correlation of certain coal beds between places 

 specified. G. C. M. 



GEOLOGY. — Sulphur deposits and beach placers of southwestern Alaska. 

 A. G. Maddren. U. S. Geol. Survey, Bull. 692-E. Pp. 37 

 (283-319), pis. 2, figs. 6. 1919. 



Sulphur deposits: Sulphur-bearing deposits at three localities in 

 southwestern Alaska — in the crater of Makushin Volcano on Unalaska 

 Island, on Akun Island, and near Stepovak Bay on the Alaska Penin- 

 sula, are of the volcanic type termed solfataras— that is, they are surface 

 deposits formed by sublimation from hot sulphurous volcanic vapors. 

 They are situated in the belt of active and quiescent volcanoes that 

 extends throughout the Alaska Peninsula, the Aleutian Islands, and 

 Japan. 



Makushin Volcano, about 6,000 feet in altitude, is in the northern 

 part of Unalaska Island, about 12 miles west of Dutch Harbor. The 

 floor of the crater is 300 to 500 feet below the higher crags of the rim, 

 but the floor of the basin is exposed only in an area of 20 to 30 acres, 

 where the sulphur deposits occur. Except in this bare area the basin 

 is occupied by glacial ice and snow. It is evident that the main solfa- 

 taric area is kept bare by subterranean heat. As a whole the sulphur- 

 bearing deposit is earthy and appears to be composed chiefly of siliceous 

 residual products of rock decomposition that have resulted from the 

 highly corrosive chemical action of the hot solfataric vapors on the 

 basalt. The richer deposits of sulphur occur within 2 feet of the sur- 

 face, but there is also more or less finely divided sulphur disseminated 

 to a depth of at least 16 feet. The commercial bodies of sulphur in this 

 deposit are clearly surficial. The percentage of sulphur at the surface 

 does not indicate that rich deposits exist at depth, as is usually believed 

 by the optimistic prospector. 



The sulphur at Akun Island deposit occurs chiefly in the form of 

 crystalline incrustations one-sixteenth to one-eighth of an inch thick 

 on the walls of narrow crevices and small cavities in the porous earthy 

 surface zone. 



