cuks.xiv. Porphyritic Clay stone Conglomerate. 475 



never show any signs of passing into masses of sedi- 

 mentary origin : they occur both in great and small 

 intrusive masses, and likewise in strata alternating with 

 those of the porphyritic conglomerate, and with the 

 planes of junction often quite distinct, yet not seldom 

 blended together. In some of these intrusive masses, 

 the porphyries exhibit, more or less plainly, a brecciated 

 structure, like that often seen in volcanic masses. These 

 brecciated porphyries could generally be distinguished 

 at once from the metamorphosed, porphyritic breccia- 

 conglomerates, by all the fragments being angular and 

 being formed of the same variety, and by the absence 

 of every trace of aqueous deposition. One of the por- 

 phyries above specified, namely, the greenstone porphyry 

 with large tabular crystals of albite, is particularly 

 abundant, and in some parts of the Cordillera (as near 

 St. Jago) seemed more common even than the purplish 

 porphyritic conglomerate. Numerous dikes likewise 

 consist of this greenstone porphyry ; others are formed 

 of various fine-grained trappean rocks ; but very few 

 of clay stone porphyry : I saw no true basaltic dikes. 



In several places in the lower part of the series, but 

 not everywhere, thick masses of a highly feldspathic, 

 often porphyritic, slaty rock occur interstratified with 

 the porphyritic conglomerate : I believe in one or two 

 cases blackish limestone has been found in a similar 

 position. The feldspathic rock is of a pale grey or 

 greenish colour ; it is easily fusible ; where porphyritic, 

 the crystals of feldspar are generally small and vitreous ; 

 it is distinctly laminated, and sometimes includes 

 parallel layers of epidote ; l the lamination appears to 



1 This mineral is extremely common in all the formations of Chile ; 

 in the gneiss near Valparaiso and in the granitic veins crossing it, in 

 the injected greenstone crowning the C.of Quillota, in somegranitic 

 porphyries, in the porphyritic conglomerate, and in the feldspathic 

 clay-slates. 



