504 Section by the Cumbre Pass, paet n. 



detail an analogous pile of strata. These vertical beds 

 are abruptly succeeded by others [B], of apparently 

 nearly the same nature but more metamorphosed, alter- 

 nating with porphyries and limestones ; these dip for a 

 short space westward, but there has been here an extra- 

 ordinary dislocation, which, on the north side of the 

 road, appears to have determined the excavation of the 

 north and south valley of the R. de las Cuevas. On 

 this northern side of the road, the strata [JB] are pro- 

 longed till they come in close contact with a jagged 

 lofty mountain [D] of dark-coloured, unstratified, in- 

 trusive porphyry, where the beds have been more highly 

 inclined and still more metamorphosed. This moun- 

 tain of porphyry seems to form a short axis of elevation, 

 for south of the road in its line, there is a hill [C] 

 of porphyritic conglomerate with absolutely vertical 

 strata. 



We now come to the Gypseous formation : I will 

 first describe the structure of the several mountains, and 

 then give in one section a detailed account of the nature 

 of the rocks. On the north side of the road, which here 

 runs in an east and west valley, the mountain of por- 

 phyry [D] is succeeded by a hill [E] formed of the 

 upper gypseous strata tilted, at an angle of between 

 70° and 80° to the west, by an uniclinal axis of elevation 

 which does not run parallel to the other neighbouring 

 ranges, and which is of short length ; for on the south 

 side of the valley its prolongation is marked only by a 

 small flexure in a pile of strata inclined by a quite 

 separate axis. A little farther on the north and south 

 valley of Horcones enters at right angles our line of 

 section ; its western side is bounded by a hill of 

 gypseous strata [F], dipping westward at about 45°, 

 and its eastern side by a mountain of similar strata 

 [G] inclined westward at 70°, and superimposed by an 



