228 The Americaji Geologist. October, i898 
in their crystal flasklets. The building advances, the cooling 
nucleus contracts, the cold and solid crust outside, being un- 
supported, sinks and is crushed. You hear, as it were, the 
creaking of the massive globe as its crystalline particles yield 
before the inconceivable earth-force. Then — in that time, 
not of disaster and catastrophe, but of slow, imperceptible 
evolution — were graven on stone those mystic characters 
which the microscope has interpreted to you this evening. 
[Contributions to tlie Mineralogy of Minnesota. I.] 
NOTE ON THE CHARACTERS OF MESOLITE 
FROM MINNESOTA.* 
By N. H. WiNCHBLL, Minneapolis, Minn. 
Mcsolite. The most conspicuous, and the most collected 
of all the Minnesota zeolites is mesolite. It has been wide- 
ly distributed from Grand Marais and from other points 
west from Grand Marais, under the name thomsonite. 
.Some of the specimens collected by the State Geological 
Survey in 1877 and 1878 were examined by Peckham and 
Hall (Am. Jour. Sci. XIX, 122, 1880), and from chemical 
characters were considered thomsonite and that designa- 
tion has been followed by the; survey in all later reports. 
This mineral is usually white, but varies from white to pink 
and to green, these colors alternating in superficial bands 
forming colored circlets or rosettes which with its hardness 
have rendered this mineral a gem of considerable beauty 
and value. 
It i's strongly radiated in fine fibres, which are long and 
rigid, in this respect differing from thomsonite, whose fibres 
are coarser and somewhat irregular in direction and shape. 
Specific gravit}' is 2.26. 
Optic Characters. Sections cut perpendicular to the fibres 
give the greatest light. Those parallel to the fibres are 
sometimes almost invisible in certain positions, especially 
in sections rather thin, owing to the very low power of 
*This and other examinations of the rocks and minerals of Minneso- 
ta were done primarily in the laboratory of Prof. A. Lacroix, Museum 
d'Histoire Naturelle, Paris, and with his assistance, for which the writer 
wishes to testify his gratitude. 
