276 EEPOET OF NATIONAL MUSEUM, 1899. 



what resembling- unglazed porcelain (Specimen No. 16070, from Gilroy, 

 California), and more rarely crystalline granular, like limestone or 

 dolomite (Specimen No. 48273, U.S.N.M., from Wells Island). 



It is hard (3.5 to 4.5) and brittle, with a vitreous luster, and is 

 unacted upon by cold, but dissolves with brisk effervescence in hot 

 hydrochloric acid. 



Localities and mode of occurrence. — Most commonly the mineral is 

 found in the form of irregular veins in serpentinous and other magne- 

 sian rocks, being a decomposition product either of the serpentine 

 itself or of the original rock from which the serpentine is derived. It 

 is also found in granular aggregates disseminated throughout serpen- 

 tinous rocks. It is stated by Dana to occur associated with gypsum. 



Prof. W. P. Blake has described^ immense beds of very puremag- 

 nesite as occurring in the foothills of the Sierra Nevadas, between Four 

 and Moore creeks, in what is now Tulare County. The beds are from 

 1 to 6 feet in thickness and are interstratified with talcose and chloritic 

 schists and serpentine. Mr. H. G. Hanks, who has since inspected 

 these deposits, reports them as existing in several hills or low moun- 

 tains, the mineral cropping out boldly in distinct and clearly marked 

 veins, varying from 2 inches to 4 feet, and of a maximum length, as 

 exposed, of 500 feet. In section 5, T. 15 S., R. 21 E., Fresno County, 

 California, there is stated^ to be a large vein of the material averaging 

 10 feet in width, incased in hornblendic and micaceous shales. A 

 white marble-like crystalline granular variety has been found in the 

 form of drift bowlders on an island in the St. Lawrence River near the 

 Thousand Islands Park. (Specimen No. 48273, U.S.N.M.) According 

 to Canadian geologists magnesite forming rock masses occurs associ- 

 ated with the dolomites, serpentines, and steatites of the eastern town- 

 ships of Quebec. In Bolton it occurs in an enormous bed resembling 

 crystalline limestone in appearance. An analysis of this yielded: Car- 

 bonate of magnesia, 59.13 per cent; carbonate of iron, 8.72 per cent; 

 silica, 32. 20 per cent. In the township of Sutton a slaty variety yielding 

 as high as 80 per cent of carbonate of magnesium occurs admixed with 

 feldspar and green chromiferous mica. In Styria the material lies in 

 Silurian beds consisting of argillaceous shales, quartzites, dolomites, 

 and limestones, resting upon gneiss. The extensive deposit of ^ mag- 

 nesite occurring associated with Subcarboniferous limestones in the 

 Swiss Tyrol is regarded by M. Koch^ as due to a decomposition of 

 the original limestone through percolating magnesia-bearing solutions. 

 Magnesia being the stronger base replaces the lime, which is carried 

 awaj^ in solution. 



The chief localities of magnesite, native and foreign, are as fol- 



1 Pacific Railroad Reports, V, p. 308 



2 Tenth Annual Report of the State Mineralogist of California, 1890, p. 185. 



3 Zeitschrift der Deutschen Geologischen Gesellschaft, XLV, Pt. 2, 1893, p. 294. 



