284 THE GEOLOGY OF MINNESOTA. 



[Quartzyte. Gabbro. 



in the rock has most probably been induced by the eruptives which are in contact 

 with it, as is evidently the case with the quartzytes of the Animikie just to the east 

 on Pigeon point. However, the change from sandstone to quartzyte (by the growth 

 of the quartz grains) sometimes occurs in beds that have not been subjected to the 

 influence of any eruptive or to any "metamorphosing" action. There is, in this 

 section, one conspicuous grain of zircon. It is highly refractive and doubly refractive, 

 showing red of two orders, the highest color being green. It is thus distinguished 

 from rutile. It has parallel extinction. u. s. a. 



No. 257. QUAKTZYTE. (Micaceous.) 



" Gray, thinly-bedded, hard, quartzyte, styled siliceo-argillaceous shale by Norwood; at a short distance 

 having the aspect of a bedded slate, probably belonging to the slate formation of No. 252; from the west side of 

 Hat point [sec. 11, T. 63-6 E.] near the extremity, overlain by the next. On the east side of the point can be 

 seen numerous dikes cutting this rock, which probably has a thickness of 500 feet." 



Ref. Annual Report, ix, pages 61-63. 



Meg. A hard, compact, very fine-grained quartzyte, dark gray in color. It 

 contains a considerable amount of a silvery micaceous mineral. 

 No section. 



Age. Animikie. u - s - - 



No. 258. GABBRO (with olwint). 



East side of Hat point, overlying or cutting No. 257 (Animikie slate). Basaltic trap-rock, rising at least 

 150 feet, and finally culminating in the summit of mount Josephine further north. (See No. 1829.) 

 Kef. Annual Report, ix, page 62; Bulletin ii, page 105. 



Mic. The feldspar is quite pure. A grain cut nearly perpendicular to n f has 

 extinction 55, according to the method of Fouque for determining the feldspars cut 

 perpendicular to the axes of elasticity.* If the section were exactly perpendicular 

 to n f this measurement would indicate anorthite, but, allowing for the slight obliquity, 

 it is only an evidence of a very basic feldspar, and can safely be named lalradorite 

 or labradorite-bytownite. 



There is some difficulty in distinguishing the olivines, which preceded the 

 feldspars in origination, from those augites which also preceded or accompanied the 

 feldspars, since the cleavages of the latter are not always evident. They both 

 possess irregularly rounded outlines, independent of the forms of the feldspars, and 

 are similarly refractive and doubly refractive. The olivines, however, when perpen- 

 dicular to an axis of elasticity, have very indistinct cleavage parallel to one or both 

 of the threads of the ocular when in extinction; in other positions their cleavages 

 are very irregular, while the augites, on the other hand, always show some straight 

 cleavages, and occasionally a diallagic structure. They frequently manifest those 



* In the employment of this method the extinction angle is always read from the vertical thread of the ocular after bringing 

 the optic plane into agreement with it. This is conventionally chosen by M. FouquS in order to make the readings comparable 

 and consistent. This feldspar, on np, has an extinction angle on the horizontal thread of 34. Bulletin de la Societt de Miniralogie 

 Franfaise, 1894, vol. xvi, p. 428. 



