424 DESCRIPTIVE GEOLOGY. 



Prof. J. Lawrence Smith has pubHshed an analysis of an alum from 

 this locality,^ with the following results: 



Alumina 10.40 



Magnesia 5.94 



Manganese 2.12 



Oxide of iron 0.15 



Potassa 0.20 ' 



Water 46.00 



Sulphuric acid 35.85 



100.66 



In the last edition of his Mineralogy, Professor Dana has classed this 

 alum under the name of Bosjemannite, a mangano-magnesium alum. The 

 analysis made by Mr. Woodward, however, shows no manganese, but a 

 very large percentage of magnesia, and contains all the impurities gathered 

 with the alum at the locality, which appears to be more closely related to 

 pickeringite, a magnesium alum mixed with some epsom salt, while the 

 needle-shaped crystals, analyzed by Professor Smith, were not procured at 

 Alum Bay, but were a product of recrystallization. 



Along the east side of the range, the cliffs in general come nearly 

 to the water's edge, and there occur a great number of alkaline and brack- 

 ish springs, which issue out of the limestone strata near the level of the 

 lake. On the west side, the hills slope off more gently, and the lake- 

 borders are occupied by a strip of Quaternary soil, which gradually widens 

 toward the north. A few miles below Flat Rock Point is a fine spring of 

 pure water. To the west of the railroad pass is a low north and south 

 Quaternary valley, which is separated from the lake by a long low table- 

 land of black basalt, extending about 10 miles in a northwest direction, and 

 abutting upon the lake, at its northern extremity, in an abrupt low preci- 

 pice. A similar basalt table-land rises slightly out of the Quaternary plain, 

 and forms the southern end of the Hansel Mountains, to the north of Mon- 

 ument Station. 



^Arn. Jour, of Sci., 2(1 series, 18, 379. 



