PLATE V. 



Fig. 1. Peridotite, — Lherzolite. Colusa Co., California. 



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This represents one of the earlier stages in the alteration of a peridotite, showing a fissured granular 

 mass of olivine, enstatite, and diallage traversed by a network of pale grayish serpentine, 

 which borders the fissnres. The mass is traversed by brown bands of serpentine, containing 

 iron-ore dnst along the medial lines. Dark grains of picotite or chromite lie in the upper 

 part of the figure 129-131 



Fig. 2. Peridotite, — Lherzolite. Colusa Co., California. 



This shows a further alteration in the same type of rock as Fig. 1. In this the outline of the 

 olivine can be distiiigui.shed by the yellow serpentine bands, while a later formation of ser- 

 pentine shows in the orange-brown interior portions which retain in part grains of colorless 

 unaltered olivine. The brown serpentine bands with their medial line of iron-ore dust are 

 more abundant and better marked than in Fig. 1 ; while nnich of this secondary black dust 

 is disseminated through the section 131, 132 



Fig. 3. Peridotite, — Lherzolite. Colusa Co., California. 



The in-incijial portion of the figure represents a crystal of enstatite from the same section as that 

 gi\-eii ill Fig. 2. The cleavage lines with their bordering gray and lirown alteration products 

 run more or less vertically, — the latter containing considerable fine lilack ore-dust. On the 

 right and left of the upper portion of the figure are shown portions nf serpen tinized olivine, 

 like tliat given in Fig. 2. The two portions are connected by a yellowish branching vein 

 of serjientine. The dark brown and black grains are picotite or iron ores 131,132 



Fig. 4. Peridotite, — Serpentine. La Vega, San Domingo. 



This indicates a further stage of alteration than that shown in Fig. 2. The brown bands with 

 their medial ore-dust remain, and are connected by finer brown bands marking the fissures 

 in the original olivine ; while the interstitial olivine has been replaced by yellow sei'peiitine. 

 Towards the bottom of the figure, on the right and left, are represented two grayish-white 

 altered eustatites. The series is continued in Figs. 2, 4, and 5 of Plate VI,, and in Fig. 2 

 of Plate VII 154 



Fig. 5. Peridotite, — Serpentine. High Bridge, Nf.w Jersey. 



A grayish-white mass of serpentine containing disseminated dark iron-ore grains and dust ; and 

 traversed by a band of serpentinized enstatite or diallage crystals, which are surrounded and 

 cut by a brown serpentine holding black ore-dust 156, 157 



Fig. 6. Peridotite, — Serpentine. High Bridge, Kew Jersey. 



This is from the same section as Fig. 6, and contains the same serpentine groundmass which, in 

 places, is stained yellow. Scattered through the groundmass are iron ores and brown ser- 

 ]ientine pseudomorphs after olivine containing ore-dust, and showing part of the original 

 olivine fissures by the traversing bands of grayish-white serpentine 156,157 



