PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. '249 



Sandstone.) 



uniformly with mesolite and partly with thomsonite. Such intergrowth appears 

 also in No. 163A. 



Bowlingite in this rock manifests definite characters (See No. 162). There is, 

 distributed amongst the other minerals of this rock in the manner of olivine, a mineral 

 that has resulted from the alteration of olivine. It is idiomorphic and earlier than 

 the augite or than the feldspar. It is sometimes surrounded entirely by the augite. 

 When cut favorably it shows two cleavages, but usually only one, and it then is dis- 

 tinctly and rather strongly absorptive, the darker shade recurring when the cleavage 

 is parallel with the principal section of the polarizer. There are also irregular 

 coarser fissures. The ordinary color of the mineral is greenish brown, or yellowish, 

 and it could be mistaken for chlorite when it is not well formed. In nearly every 

 optic character it can be identified with the mineral described byLawsonasidditigsite. 

 It is not fibrous, but distinctly cleaved parallel to definite chrystallographic char- 

 acters. The optic plane is perpendicular to the easy cleavage, and the acute 

 bisectrix (n p ) is shown in sections parallel to this cleavage, making the mineral 

 negative. This axial angle is so small that its interference figure is almost a perma- 

 nent black cross; but on rotation its arms are seen to fluctuate a little from perpen- 

 dicularity to each other, the alternate angles becoming less or greater than 90. The 

 separation of the hyperbolas can hardly be observed. In sections transverse to the 

 easy cleavage the direction of the cleavage lines is positive with respect to the axis 

 (n e ) of the quartz plate. Its double refraction is about the same as that of augite, 

 but its refraction is less. 



Two sections. 



Aye. Manitou. N. H. w. 



No. 194. SANDSTONE. (Brmvn. ) 



" Brown sandstone, from Good Harbor bay [sec. 34, T. 61-1 W.]; aluminous; by making measurement 

 along the beach the outcrop is found to extend 1,400 feet, with an average dip of S^ toward the lake; by trigono- 

 metrical calculation the thickness of the strata is ascertained to be 206.9 feet, as exposed, but the thickness must 

 be considerably more, owing to the non-exposure of rock in an interval of nearly 1,000 feet before the underlying 

 finer beds appear in the beach further north. This is probably the equivalent of the sandstone at Cariboo 

 point, but may be another stratum. It is very frail and although sometimes a little slaty it will easily fall to 

 pieces if taken in the hand." 



Bef. Annual Report, ix, page 51. 



Mf//. A fine-grained, dark brown, rather poorly cemented sandstone. Some of 

 the grains are seen to be rounded, while others are angular. All of the grains are 

 coated with iron oxide. The rock effervesces with hydrochloric acid, showing consid- 

 erable calcite in the cement. No section. 



Age. Potsdam. u. s. G. 



Remark. From general structural considerations this belt of sandstone seems 

 to be distinct from that at Cariboo point, both being, however, in the Potsdam. 



N. H. w. 



