422 Bakia, Brazil : paet n. 



CHAPTEE XIII. 



PLUTONIC AXD METAMORPHIC EOCKS : — CLEAVAGE AND 



FOLIATION. 



Brazil, Bahia, gneiss with disjointed metamorphosed dikes — Strike 

 of foliation — Rio de Janeiro, gneiss-granite, embedded fragment 

 in, decomposition of — La Plata, metamorpMc and old volcanic rocks 

 of — S. Ventana — Clay stone porphyry formation of Patagonia ; 

 singular metamorphic rocks; speudo-dikes — Falkland Islands, 

 palceozoic fossils of — Tierra del Fuego, clay-slate formation, 

 cretaceous fossils of; cleavage and foliation ; form of land — Chonos 

 Archipelago, mica schists, foliation disturbed by granitic axis ; 

 dikes — Chiloe — Concepcion, dikes, successive formation of — Central 

 and Northern Chile — Concluding remarks on cleavage and folia- 

 tion — Their close analogy and similar origin — Stratification of 

 metamorpMc scliists — Foliation of intrusive rocks — Relation of 

 cleavage and foliation to the lines of tension during metamorphosis. 



The met amorphic and plutonic formations of the several 

 districts visited by the Beagle will be here chiefly 

 treated of, but only such cases as appear to me new, or 

 of some special interest, will be described in detail ; at 

 the end of the chapter I will sum up all the facts 

 on cleavage and foliation, — to which I particularly 

 attended. 



Bahia, Brazil: lot. 13° south. — The prevailing 

 rock is gneiss, often passing, by the disappearance of 

 the quartz and mica, and by the feldspar losing its 

 red colour, into a brilliantly grey primitive green- 

 stone. Not unfrequently quartz and hornblende are 

 arranged in layers in almost amorphous feldspar. 



