306 THE GEOLOGY OP MINNESOTA. 



[Oalcite, quartz, etc. 



by the crystal in general. The true diallagic structure does not destroy the orienta- 

 tion of the augite, but in this case the fibrated mineral has an orientation different 

 from that of the original augite. 



Another section was made of this rock for the purpose of studying more fully 

 the changes undergone by the augite. There are four facts that appear distinctly in 

 the course of this change: (1) The augite changes to what may be called diallage, 

 by the loss of the prismatic cleavages and the acquirement of a cleavage parallel to 

 100. This can be seen in a single grain, in which the centre is still augite with its pris- 

 matic cleavages at right angles, and in which the surrounding mass is still augite, 

 having the same extinction but only the cleavage 100. (2) A cleavage is developed 

 parallel to the base 001 which appears at first imperfectly and in short cracks. (3 ) Par- 

 allel with this basal cleavage is a finely fibrous alteration product, called diallage 

 by Wadsworth (Bulletin ii, plate VII, figure 1), which is the so-called ririi/ite of 

 numerous authors. (4) This substance, which has no longer the orientation of the 

 augite and cannot be considered diallage, is further altered, by a new crystallization, 

 into amphibole- whose cleavages, in the section represented by Wadsworth, are 

 parallel to the prismatic cleavages of the original augite. 



Biotife can be distinguished by its pleochroism, though it is not always brown. 



The chlorite is decorated with the characteristic dark halos. It is about hexag- 

 onal, and gives a black cross in convergent light. 



Bowlingite seems to have been generated in abundance, the product of changed 

 olivine, which is now wholly wanting. 



Hornblende, a uralitic product of change from the pyroxene is scattered in grains 

 that vary much in size. It is prevailingly of a faint green color, distinctly cleaved 

 and pleochroic. 



(Jiiartz is common both as individual grains of considerable size, of secondary 

 origin, and as pegmatitic growths in the feldspars. 



Apatite is seen in the quartz grains and in the altered feldspar. 



Two sections. 



Age. Cabotian. N. H. w. 



No. 301. CALCITE, QUARTZ, ETC. (Vein material.) 



"Vein matter from Kindred and Baker's shaft on the White Rose vein, near Arrow lake in Canada. This 

 is about one and a quarter miles north of the east end of the first lake [Rove lake] west of Mountain lake.'' 

 Ref. Annual Report, vii, page 17; Annual Report, ix, pages 77, 78. 



Meg. Calcite and quartz with some chalcocite (?) and pyrite and rock frag- 

 ments. 



Mic. The section shows ccilcite and ijnartz with particles of the rock which is 

 black and opaque. One section. 



Age. Vein in Animikie rocks. u. s. G. 



