PREFACE XIU 



without any quartz. This occurs in large masses, closely re- 

 sembling in external form granite or syenite, and is interesting 

 from its perfect similarity to andesite which forms the great 

 injected axes of the Cordillera of Chili. 



The stratification of the clay-slate is generally very obscure, 

 whereas the cleavage is remarkably well defined, striking in the 

 extreme east of the island W. and E. and even W.S.W. and 

 E.N.E.; over the main portion, including the Darwin Range, 

 W.N.W. and E.S.E. ; in the central and western portion of the 

 Strait of Magellan N.W. and S.E. ; and north of the Strait 

 nearly N. and S. 



Of the islands to the extreme south, it is interesting to note 

 that on Wollaston Island slate and grauwacke can be distinctly 

 traced passing into felspathic rocks and greenstones, including 

 iron pyrites and epidote, but still retaining traces of cleavage 

 with the usual strike and dip. One such metamorphosed mass 

 is transversed by large vein-like masses of a beautiful mixture 

 of green epidote, garnets, and white calcareous spar. On the 

 northern portion of this same island, there are various ancient 

 submarine volcanic rocks, consisting of amygdaloids with dark 

 bole and agate, — of basalt with decomposed olivine, — of 

 compact lava with glassy felspar, — and of a coarse conglomerate 

 of red scoriae, parts being amygdaloidal with carbonate of lime. 

 The southern part of Wollaston Island and the whole of 

 Hermite and Horn Islands are formed of cones of greenstone. 



The external features of Tierra del Fuego are exceedingly 

 varied. There are lowland flats with vast marshes and lakes 

 more or less brackish, scrub-covered downs, bleak black peaty 

 moors, practically impenetrable forests, and regions of ever- 

 lasting snow probably never trodden by man. In the coast- 

 line, there is also much diversity. This may be low shingly 

 beach with the land dead flat behind it, or bare perpendicular 

 clifl* washed at foot by the sea, or solid jagged rock overgrown 

 to high-tide mark with impermeable thorn scrub, or else pre- 

 cipitous mountain covered with forest or glacier to the very ocean. 



