chap. xiii. Chonos Archipelago, 45 1 



slightly antkracitic schist, which soils paper, and be- 

 comes white under a great heat, and then fuses. Thin 

 layers of feldspar, swelling at intervals into well crystal- 

 lised kernels, are sometimes included in these black 

 schists ; and I observed one mass of the ordinary black 

 variety insensibly lose its fissile structure, and pass into a 

 singular mixture of chlorite, epidote, feldspar, and mica. 

 Great veins of quartz are numerous in the mica-schist ; 

 wherever these occur the folia are much convoluted. 

 In the southern part of the Peninsula of Tres Montes, 

 a compact altered feldspathic rock with crystals of 

 feldspar and grains of quartz is the commonest variety ; 

 this rock 1 exhibits occasionally traces of an original 

 brecciated structure, and often presents (like the altered 

 state of Tierra del Fuego) traces of cleavage-planes, 

 which strike in the same direction with the folia of 

 mica-schist farther northward. At Inchemo Island, a 

 similar rock gradually becomes granulo-crystalline and 

 acquires scales of mica ; and this variety at S. Estevan 

 becomes highly laminated, and though still exhibiting 

 some rounded grains of quartz, passes into the black, 

 glossy, slightly anthracitic schist which, as we have 

 seen, repeatedly alternates with and passes into the 

 micaceous and chloritic schists. Hence all the rocks 

 on this line of coast belong to one series, and insensibly 

 vary from an altered feldspathic clay-slate into largely 

 foliated, true mica-schist. 



The cleavage of the homogeneous schists, the folia- 

 tion of those composed of more or less distinct minerals 

 in layers, and the planes of alternation of the different 

 varieties or so-called stratification are all parallel, and 

 preserve over this 200 miles of coast a remarkable 



1 The peculiar, abruptly conical form of the hills in this neigh- 

 bourhood, would have led any one at first to have supposed that they 

 had been formed of injected or intrusive rocks. 



