615 



HI. FORMATION OF SERPENTINE AND DIORITE 

 (GREENSTONE OF JUNCALITO). 



We have indicated above, a layer of granati- 

 ferous serpentine inclosed in the gneiss of Bue- 

 navista, or perhaps superposed on that rock; 

 we here find a real soil of serpentine, alternating 

 with diorite, and extending from the ravine of 

 Tucutunemo as far as Juncalito. The diorite 

 forms the great mass of this soil ; it is of a dark- 

 green colour, granular with small grains, and 

 destitute of quartz ; its mass is formed of small 

 crystals of feldspar, intermixed with crystals 

 of amphibol. This rock of diorite is covered 

 at its surface, by the effect of decomposition, 

 with a yellowish crust like that of basalts, and 

 dolerites. Serpentine of a dull olive -green, and 

 smooth fracture, mixed with blueish steatite, 

 and amphibol, presents, like almost all the co- 

 ordinate formations of diorite and serpentine (in 

 Silesia, at Fichtelgelirge, in the valley of Bai- 

 gorry, in the Pyrenees, in the isle of Cyprus, 

 and in the copper mountains of circumpolar 

 America)*, traces of copper (Vol. iv, p. 279). 

 Where the diorite, partly globular, draws near 

 the green slate of Malpasso, real beds of 

 green slate are found inclosed in diorite. 



* franklin's Journal to the Polar Sea, p. 529. 



