454 Chonos Archipelago. part n. 



crown !) of the mica-schist, foliated with the same 

 northerly dip. On the broad summit, as far as the 

 southern crest, there is much mica- slate, in some places 

 even 400 feet in thickness, with the folia all dipping 

 north, at angles varying from 5° to 20°, but sometimes 

 mounting up to 30°. The southern flank consists of 

 bare granite. The mica-slate is penetrated by small 

 veins l of granite, branching from the main body. 

 Leaving out of view the prevalent strike of the folia in 

 other parts of this archipelago, it might have been 

 expected that here they would have dipped N. 28° E., 

 that is, directly from the ridge, and, considering its 

 abruptness, at a high inclination ; but the real dip, as 

 we have just seen, both at the foot and on the northern 

 flank, and over the entire summit, is at a small angle, 

 and directed nearlv due north. From these considera- 

 tions it occurred to me, that perhaps we here had the 

 novel and curious case of already inclined laminae 

 obliquely tilted at a subsequent period by the granitic 

 axis. Mr. Hopkins, so well known from his mathe- 

 matical investigations, has most kindly calculated the 

 problem : the proposition sent was, — take a district 

 composed of lamina?, dipping at an angle of 40° to 

 W. 19° S., and let an axis of elevation traverse it in an 

 E. 28° S. line, what will the position of the laminae be 

 on the northern flank after a tilt, we will first suppose, 

 of 45° ? Mr. Hopkins informs me, that the angle of 

 the dip will be 28° 31', and its direction to north 

 30° 33' west. 2 By varying the supposed angle of the 



1 The granite within these veins, as well as generally at the 

 junction with the mica-slate, is more quartzose than elsewhere. The 

 granite, I may add, is traversed by dikes running for a very great 

 length in the line of the mountains ; they are composed of a some- 

 what laminated eurite, containing crystals of feldspar, hornblende, 

 and octagons of quartz. 



2 On the south side of the axis (where, however, I did not see any 

 mica-slate) the dip of the folia would be at an angle of 77° 55', 



