170 PERIDOTITE. 



the whole mass is traversed by brown veins bearing iron dust along the 

 medial line. Figure 2 shows further progress in the change ; the brown 

 veins increase in number and strength, and the ferruginous medial line 

 becomes more strongly marked. Bordering these veins are bands of j'ellow 

 serpentine, which in their turn are fringed on the inner side by orange, 

 yellow, and brown serpentine, which again encloses grains of the still un- 

 altered olivine. In figure 4 the change has progressed still further. The 

 same brown veins with their ferrughious backbone are to be seen, but the 

 yellow serpentine has engrossed the remainder, cutting out the orange-yel- 

 low serpentine and the still unchanged olivine grains seen in figure 2. 

 Towards the base of figure 4 and on the right and left are to be seen the 

 remains of two partly-altered grayish pyroxenes. Plate VI. figure 4 shows 

 a still further change; in which the brown veins and the interstitial por- 

 tions are only distinguished by slight shades of color. Inclosed in this is an 

 enstatite, which retains its characteristic optical characters, but still it is 

 altered and filled in by magnetite grains, which have separated out during 

 the process of alteration. Figure 2 shows still farther change, in which 

 the brown veins are only represented by their intermedial line of magnetite 

 dust, which is bordered by a pale-yellov/ish or nearly colorless serpentine, 

 holding interstitial rounded patches of serpentine, representing the last- 

 altered olivine cores. 



Plate V. figure 3 shows the mode of alteration in the enstatite, taken 

 from the same section as figure 2. At the left and right of the upper por- 

 tion of the figure are to be observed portions of the altered olivine mass as 

 shown in figure 2, while a yellowish serpentine vein joins the two parts, 

 and cuts the enstatite. Along the cleavage-planes of the enstatite the 

 greenish and yellowish secondary product extends, while the interme- 

 diary portions are imchanged. Plate VII. figure 1 represents a still greater 

 change in a crystal of enstatite from the same section. The colors are 

 deeper, and fewer unchanged, intermediary portions exist, while the cross 

 cleavage is w^ell shown by the yellowish-green serpentine bands following 

 its planes. 



In Plate V. figure 5, we see the remains of serpentinized diallage crys- 

 tals, showing optically the characters of serpentine surrounded by brown 

 bands and all inclosed in pale-yellow and colorless serpentine. In figure 6 is 

 shown another portion of the same section, in which the change has proceeded 

 to a greater extent, leaving only the brown serpentinous masses to represent 



