240 THE GEOLOGY OP MINNESOTA. 



[M.-solite. Sandstone. Conglomerate. 



Mfij. It has the appearance, being broken, of having been at least six inches in 

 diameter, and of a plano-convex form. In the central portion of this mass is an 

 irregular crystalline form of calcite an inch and a half in greater dimension. 



Mic. The axial angle about n s in the heulandite is small and about 50. 



Remark. In the field this crystalline mass was taken for stilbite. N. H. w. 



No. 173B. MESOLITE. 



Prom the beach in the bay on section 28, near No. 173. 

 Ref. Annual Report, ix, page 46. 



NC<I. A white, strongly-radiated mineral resembling that of No. 163A,but finer. 



Mic. Double refraction very low; indeed, the fact of extinction can hardly be 

 observed without mounting the powder in Canada balsam, when it is seen that the 

 fibres extinguish parallel with the threads, and have a positive elongation. A micro- 

 chemical test shows the presence of soda and lime. The mineral may be taken to 

 be, therefore, mesolite. 



Age. Manitou. N. H. w. 



No. 174. SANDSTONE. (Ferruginous.) 



Sec. 12, T. 59-4. Coast of lake Superior at five miles east of Temperance river. 

 Ref. Annual Report, ix, page 46. 



Mcy. A ferruginous and feldspathic sandstone, sprinkled with scattered small 

 secondary crystals of laumontite. This sandstone is dispersed through a breccia or a 

 conglomerate which resulted probably from the rapid disintegration of an eruptive 

 of the prevalent kind, under the action of the ocean's waters on a lava flow. The 

 associated trap, amygdaloid and sandstone are in bluffs that rise from twenty to 

 forty feet. 



Mir. Thin sections of the trap show a finely ophitic structure, the white 

 plagioclase needles piercing the darker constituents in a beautiful and characteristic 

 manner, the latter being ferrated. In the interstices is found also the same soft, 

 radiated decomposition product as mentioned already in connection with No. 162, as 

 well as coarser amygdaloids of the common zeolites. 



One section of the associated diabase. 



Af/c. Potsdam. N. H. w. 



No. 175. CONGLOMERATE. 



About six miles east of Temperance river. 

 Ref. Annual Report, ix, pages 47, 48. 



This rock is distinctly conglomeratic, containing lumps of brown 

 amygdaloid, the amygdules being of laumontite and calcite. These lumps are 

 contained in a ferruginous and aluminous red sandstone, which really constitutes 

 less than one-half of the mass. These beds of conglomerate are about six feet thick, 



