chap. xiv. Section of the Portillo Chain, 495 



probably belong to an older formation, almost over- 

 whelmed and penetrated by the red granite. 



On the crest I saw also, at a short distance, some 

 coloured stratified beds, apparently like those [W] at 

 the western base, but was prevented examining them 

 by a snow-storm : Mr. Oaldcleugh, 1 however, collected 

 here specimens of ribboned jasper, magnesian lime- 

 stone, and other minerals. A little way down the 

 eastern slope a few fragments of quartz and mica-slate 

 are met with; but the great formation of this latter 

 rock [Z], which covers up much of the eastern flank 

 and base of the Portillo range, cannot be conveniently 

 examined until much lower down at a place called Mai 

 Paso. The mica-schist here consists of thick layers 

 of quartz, with intervening folia of finely-scaly mica, 

 often passing into a substance like black glossy clay- 

 slate : in one spot, the layers of quartz having disap- 

 peared, the whole mass became converted into glossy 

 clay- slate. Where the folia were best defined, they 

 were inclined at a high angle westward, that is, towards 

 the range. The line of junction between the dark 

 mica-slate and the coarse red granite was most clearly 

 distinguishable from a vast distance : the granite sent 

 many small veins into the mica-slate, and included 

 some angular fragments of it. As the sandstone on the 

 western base has been converted by the red granite into 

 a granular quartz-rock, so this great formation of mica- 

 schist may possibly have been metamorphosed at the 

 same time and by the same means; but I think it 

 more probable, considering its more perfect metamor- 

 phic character and its well-pronounced foliation, that it 

 belongs to an anterior epoch, connected with the white 

 granites : I am the more inclined to this view, from 

 having found at the foot of the range the mica-schist 

 1 « Travels/ &c, vol. p. 308. 



