PLATE VI. 



Fig. 1. Peridotite, — Serpentine. Santiago, San Domingo. 



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This shows at the base a brownish and yellowish reticulated serpentine mass, while above lie 

 yellowish and brown pseudoniorphs of serpentine after olivine grains which are surrounded 

 and cut by colorless serpentine. In all the serpentine masses, particularly the upper por- 

 tion, are disseminated black grains and dust of iron ore 153, 154 



Fig. 2. Peridotite, — Serpentine. Ltnnfield, Massachusetts. 



This forms one of a series with Figs. 1, 2, and 4 of Plate V. In this the brown serpentine bands 

 no longer appear, but their former position is marked by the lines of black iron ore. The 

 pale flesh-tint indicates serpentine which encloses the yellowish central rounded spots of 

 serpentine which has replaced the last -altered olivine grains. At the top and bottom of the 

 figure are to be seen patches of pale serpentine in which the alteration has been carried so far 

 that the yellowish portions have disappeared and the color been rendered uniform, — the con- 

 stant tendency in the serpentinization of peridotites. The black grains are the iron ores. . . 160 



Fig. 3. Peridotite, — Lherzolite, — Serpentine. Plumas Co., California. 



This shows a yellowish and grayish serpentine in which are lying black iron ore and the fibrous 



remains of enstatite crystals, which are best seen in the centre of the figure. ^ 142 



Fig. 4. Peridotite, — Lherzolite, — Serpentine. Inyo Co., California. 



This exhibits a brownish reticulated serpentine, holding in its interstices serpentine of a lighter 

 color. This belongs to the same series as Fig. 2. In the serpentine lies a large fibrous 

 crystal of altered enstatite, filled with black granules of iron ore precipitated during the pro- 

 cess of alteration. The same ore is also to be seen in the serpentine 132 



Fig. 5. Peridotite, — Serpentine. Plumas Co., California. 



This shows a grayish- white reticulated mass of serpentine containing disseminated black iron-ore 

 dust of a secondary nature ; also some larger black primary grains of iron ore. The upper half 

 of the figure is traversed by veins of yellow serpentine, one of which cuts an iron-ore grain. 158 



Fig. 6. Peridotite, — Lherzolite, — Serpentine. Plumas Co., California. 



This figure is from the same section as Fig. 3, and illustrates the formation of a serpentine vein. 

 This, in the form of a brownish-yellow obliquely banded serpentine, crosses the central por- 

 tion of the figure, while heaped up on both sides are to be seen the aggregations of expelled 

 iron ores mixed with yellow and colorless serpentine.^ 142 



1 Whitney's Auriferous Gravels, 1880, p. 459. 



