ITS MICROSCOPIC CHARACTERS. 171 



the altered minerals. Figure 1, Plate VI., shows a similar change. The 

 figure at its base possesses a character similar to that of figure 4, but in the 

 remaining portion is composed of clear, colorless serpentine, holding iron ores 

 and yeilovvish serpentine pseudomorphs after olivine gr lins. 



Figure 3 represents aserpentinized peridotite containing rejected iron ores 

 and in the central portion the remains of enstatite crystals. In figure •"> we 

 have an entire alteration of the rock to a light or colorless serpentine, filled 

 with the precipitated iron ores, and traversed by yellow ^•eins of serpentine. 

 In figure 6 is to be seen a portion of the same section as that shown in 

 figure 3. This is traversed by a yellowish, obliquelj^-banded, serpentine 

 vein, while the adjacent bordering serpentine is filled with the ferruginous 

 products rejected during the process of the formation of the serpentine vein. 

 Plate VII. figure 2 shows a peridotite in which the change has gone so far 

 that no trace remains of the original structure, while the precipitated ferru- 

 ginous products largely assume the form of a rectangular grating in the 

 yellow serpentine. 



In figure 3 of the same plate, is shown an altered Iherzolite in which 

 enstatite forms the groundwork, inclosing the olivine. The enstatite sliows 

 the usual greenish alteration along the cleavage planes and throughout much 

 of the interstitial portions. The olivine is chiefly distinguished by the 

 rejection of large quantities of magnetite dust on the borders of the grains 

 and their fissures. Sometimes the separation of the ferruginous material 

 in this form has been carried so far as to render the olivine grains nearly 

 or quite opaque. Figure 4 shows a further change in this Iherzolite, in 

 which the enstatite is partly replaced by greenish serpentinous material, and 

 partly by dolomite and other secondary products. The olivine is altered 

 and in j^art replaced by serpentine, magnetite, etc., although portions yet 

 remain unchanged. Figure 5 indicates a still further alteration in this 

 Iherzolite, and one in wdiich the enstatite and part of the olivine have been 

 replaced by a groundmass of granular dolomite. The olivine grains now 

 appear only in the greenish and brownish pseudomorphs after that mineral, 

 inclosed in the dolomite groundmdss. Figure 6 sliows a yellowish secondary 

 serpentine mass with inclosed colorless grains of unaltered olivine, and, so 

 far as this portion of the section is concerned, is closely like that shown in 

 Plate IV. figure 4, except in the former the serpentine is yellow, and in the 

 latter it is green. But in addition, there occur in the serpentine, in the 

 above-mentioned figure 6, gray and brownish particles and grains of secon- 



