44 8 . Tier r a del Fuego. paet n. 



fact, that the fine laminae of the clay-slate, where cut- 

 ting straight through the bands of stratification, and 

 therefore indisputably true cleavage-planes, differed 

 slightly in their greyish and greenish tints of colour, in 

 compactness, and in some of the laminae having a rather 

 more jaspery appearance than others. I have not seen 

 this fact recorded, and it appears to me important, for 

 it shows that the same cause which has produced the 

 highly fissile structure, has altered in a slight degree 

 the mineralogical character of the rock in the same 

 plaues. The bands of stratification, just alluded to, 

 can be distinguished in many places, especially in 

 Navarin Island, but only on the weathered surfaces of 

 the slate ; they consist of slightly undulatory zones of 

 different shades of colour and of thicknesses, and re- 

 semble the marks (more closely than anything else 

 to which I can compare them) left on the inside of a 

 vessel by the draining away of some dirty slightly 

 agitated liquor : no difference in composition, corre- 

 sponding with these zones, could be seen in freshly 

 fractured surfaces. In the more level parts of 

 Navarin Island, these bands of stratification were 

 nearly horizontal ; but on the flanks of the mountains 

 they were inclined from them, but in no instance that 

 I saw at a very high angle. There can, I think, be no 

 doubt that these zones, which appear only on the 

 weathered surfaces, are the last vestiges of the ori- 

 ginal planes of stratification, now almost obliterated 

 by the highly fissile and altered structure which the 

 mass has assumed. 



The clay-slate cleaves in the sameWXW. and ESE. 

 direction, as on Xavarin Island, on both sides of the 

 Beagle Channel, on the eastern side of Hoste Island, on 

 the NE. side of Hardy Peninsula, and on the northern 

 point of Wollaston Island; although in these two 



