230 THE GEOLOGY OP MINNESOTA. 



[Amygdaloid- 



presence of lime and soda, along with the low power of double refraction, conspire 

 to indicate that this is mesolite. 



Chemical analysis. This white mineral was analyzed by Sharpless and Winchell, with the following 

 result, which is the average of three determinations (1): 



Si0 2 46.12 40.40 



A1 2 3 29.08 26.30 



CaO - 10 - 08 9 - 60 



Na 2 2.41 5.30 



K,6 - 



H 2 O 12 -32 12.40 



Total 100.00 100.00 



In column II is shown the composition of mesolite given by Lacroix (Min. de 

 France et de ses Colonies, vol. ii, page 278). 



Age. Manitou. 



Remark. This mineral has doubtless been taken for thomsonite at several points 

 on the Lake Superior coast. This is found in the much decayed amygdaloids of the 

 Manitou in the same manner as the thomsonites of the region. Mingled with this min- 

 eral, in mammillated spherulitic forms, is a finely fibrous form of silica which has a 

 positive elongation to which, therefore, the name qi/a/izine should be given rather 

 than that of chalcedony. N. H. w. 



No. 162. AMYGDALOID. 



From the same place as No. 161. 

 Ref. Annual Report, ix, page 42. 



Meg. A brown amygdaloid, or at least with many original cavities now filled 

 with a greenish soft substance (the thalite of Owen), much decayed. Some of the 

 larger cavities contain mesolite which, about the circumference, is amorphous and 

 has the dirty greenish color of thalite, but remains hard. 



Mic. The feldspars, at least the larger ones, are completely filled with inclusions 

 resulting from decay and afford only an aggregate polarization. The smaller 

 feldspars have greater purity and more definite outward form, but still -are consid- 

 erably decayed. They are embraced ophitically in the auyite. 



The original auyite, as well as the olivine, has given place to an opaque or 

 brownish substance (in part bowlingite?), probably colored by oxide of iron. Some 

 portions of these decayed and mostly opaque grains still polarize characteristically 

 for augite, but for the most part the augite is lost. The olivine cannot be distin- 

 guished as such, but many of the opaque spots enclose central translucent areas 

 which probably represent bowlingite or the remains of olivine grains. The brownish 

 red mineral (bowlingite?) is apparently the same as seen in No. 133. 



The green substance occupies places whose shapes were determined by the 

 crystallization of the other minerals, and hence they are not round or amygdaloidal. 

 These areas were not occupied by gas, but some substance must have filled them, 



