45 6 Chiloe and Conception, pakt ii. 



intersected the volcanic formation described in the last 

 chapter. North of Tres Montes, I noticed three dikes 

 differing from each other in composition, one of them 

 having an euritic base including large octagons of 

 quartz ; these dikes, as well as several of porphyritic 

 greenstone at Vallenar Bay, extended NE. and SW., 

 nearly at right angles to the foliation of the schists, 

 but in the line of their joints. At Low's Harbour, 

 however, a set of great parallel dikes, one ninety yards 

 and another sixty yards in width, have been guided by 

 the foliation of the mica-schist, and hence are inclined 

 westward at an angle of 45° : these dikes are formed of 

 various porphyritic traps, some of which are remarkable 

 from containing numerous rounded grains of quartz. 

 A porphyritic trap of this latter kind, passed in one of 

 the dikes into a most curious hornstone, perfectly white, 

 with a waxy fracture and pellucid edges, fusible, and 

 containing many grains of quartz and specks of iron 

 pyrites. In the ninety yard dike several large, appa- 

 rently now quite isolated fragments of mica-slate were 

 embedded ; but as their foliation was exactly parallel 

 to that of the surrounding solid rock, no doubt these 

 now separate fragments originally formed wedge-shaped 

 depending portions of a continuous vault or crust, 

 once extending over the dike, but since worn down and 

 denuded. 



Chiloe Valdivia, Conception. — In Chiloe, a great 

 formation of mica-schist strikingly resembles that of 

 the Chonos Islands. For a space of eleven miles on 

 the SE. coast, the folia were very distinct, though 

 slightly convoluted, and ranged within a point of NNW. 

 and SSE., dipping either ENE. or more commonly 

 WSW., at an average angle of 22° (in one spot, however, 

 at 60°), and therefore decidedly at a lesser inclination 

 than amongst the Chonos Islands. On the west and 

 north-western shores, the foliation was often obscure, 



