chap. xv. Ravine of Jolquera. 567 



white sandstone and dark mudstone, there is a vast 

 mass of coarse, hard, red conglomerate, some thousand 

 feet in thickness, which contains much silicified wood, 

 and evidently corresponds with the great upper con- 

 glomerate at Las Amolanas : here, however, the con- 

 glomerate consists almost exclusively of pebbles of 

 granite, and of disintegrated crystals of reddish feldspar 

 and quartz firmly recemented together. In this case, 

 we may conclude that the land whence the pebbles were 

 derived, and on which the now silicified trees once 

 flourished, was formed of granite. 



The mountains near Las Amolanas, composed of 

 the cretaceo-oolitic strata, are interlaced with dikes like 

 a spider's web, to an extent which I have never seen 

 equalled, except in the denuded interior of a volcanic 

 crater : north and south lines, however, predominate. 

 These dikes are composed of green, white, and blackish 

 rocks, all porphyritic with feldspar, and often with 

 large crystals of hornblende. The white varieties 

 approach closely in character to andesite, which com- 

 poses, as we have seen, the injected axes of so many of 

 the lines of elevation. Some of the green varieties are 

 finely laminated, parallel to the walls of the dikes. 



Sixth Axis of Elevation (Valleij of Oopiapo). — 

 This axis consists of a broad mountainous mass [0] of 

 andesite, composed of albite, brown mica, and chlorite, 

 passing into andesitic granite, with quartz : on its 

 western side it has thrown off, at a considerable angle, 

 a thick mass of stratified porphyries, including much 

 epidote [N N], and remarkable only from being divided 

 into very thin beds, as highly amygdaloidal on their 

 surfaces as sub-aerial lava-streams are often vesicular. 

 This porphyritic formation is conformably covered, as 

 seen some way up the ravine of Jolquera, by a mere 

 remnant of the lower part of the cretaceo-oolitic 



