364 W. Cross — Some secondary minerals 



ersing several distinct grains will be bridged over by blue 

 fibers which possess the crystallographic orientation of the en- 

 closing grain. Small particles of brown hornblende included 

 in augite grains suffer the changes noticed and the new miner- 

 als seem in some cases to have induced a similar alteration of 

 the augite itself. The blue variety is much more common as 

 an enlargement than is the actinolite, but they frequently occur 

 side by side, with sharp boundaries between them. 



From the study of many sections of the blue amphibole it 

 appears as its most peculiar property that the axis of greatest 

 elasticity, a, lies near the vertical crystallographic axis and on 

 the opposite side from the position of c in glaucophane, common 

 hornblende, actinolite, etc. This is clearly shown by using the 

 quartz wedge as a compensator in the well known manner. 

 The axis of least elasticity, c, is also in the plane of symmetry, 

 which thus remains the plane of the optic axes as for other 

 amphiboles. The angle 6 : a is 13° to 15°. The optic angle is 

 large and in consequence the optical character of the mineral 

 could not be satisfactorily determined. Pleochroism : a = deep 

 blue, b = purple to violet, c=pale yellow. Absorption : a > b > c. 



The second material in which the blue amphibole has been 

 observed occurs half a mile north of the dike above described, 

 and is of problematic origin. In a region of fresh Archaean 

 outcrops some prospector found a peculiar exposure and ex- 

 plored it by a shaft 15 feet deep. Nothing is known of the 

 formation beyond the data afforded by this shaft. The 

 material passed through is structurally a conglomerate, the 

 greater part composed of pebbles less than one cm. in diame- 

 ter, which are dull olive-green in color and seem macroscop- 

 ically homogeneous throughout. They are imbedded in a 

 similar green matrix which contains however many particles 

 of feldspar, hornblende, biotite, and quartz, the gravelly debris 

 of the adjacent gneisses. In parts of the mass are larger 

 pebbles of gneiss or granite and a few of diorite. The surface 

 outline of this mass is obscured but it does not extend more 

 than a few yards from the shaft in any direction, and it seems 

 probable that the material is the filling of a crevice or hole in 

 the Archaean by waterworn particles. Nothing resembling it 

 was found elsewhere. As far as the present paper is concerned 

 it is only important to show that the rock is markedly + a sec- 

 ondary formation and also entirely different in origin from that 

 above described. Microscopical study shows the dull green 

 pebbles and the green part of the groundmass to consist 

 largely of calcite and quartz, and the green color to come from 

 minerals of secondary origin, to be referred to again below. 

 The grains of green or brownish hornblende of common char- 

 acteristics lying in the matrix, are seen in all stages of altera- 



