chap. xin. Central and Northern Chile. 459 



S. line; and again, during the great earthquake of 

 February 1835, the ground in this neighbourhood was 

 fissured in NW. and SE. lines ; and from the manner in 

 which buildings were thrown down, it was evident that 

 the surface undulated in this same direction. 1 



Central and Northern Chile. — Northward of Con- 

 cepcion, as far as Copiapo, the shores of the Pacific 

 consist, with the exception of some small tertiary basins, 

 of gneiss, mica-schist, altered clay-slate, granite, green- 

 stone and syenite : hence the coast from Tres Montes 

 to Copiapo, a distance of 1,200 miles, and I have reason 

 to believe for a much greater space, is almost similarly 

 constituted. 



Near Valparaiso the prevailing rock is gneiss, 

 generally including much hornblende : concretionary 

 balls formed of feldspar, hornblende and mica, from 

 two to three feet in diameter, are in very many places 

 conformably enfolded by the foliated gneiss : veins 

 of quartz and feldspar, including black schorl and well- 

 crystallised epidote, are numerous. Epidote likewise 

 occurs in the gneiss in thin layers, parallel to the folia- 

 tion of the mass. One large vein of a coarse granitic 

 character was remarkable from in one part quite 

 changing its character, and insensibly passing into a 

 blackish porphyry, including acicular crystals of glassy 

 feldspar and of hornblende : I have never seen any other 

 such case. 2 



I shall in the few following remarks on the rocks of 

 Chile allude exclusively to their foliation and cleavage. 

 In the gneiss round Valparaiso the strike of the foliation 

 is very variable, but I think about N. by W. and S. by 



1 ' Geolog. Trans.' vol. vi. pp. 602 and 617. ' Journal of Re- 

 searches ' (2nd edit.), p. 307. 



2 Humboldt (' Personal Narrative,' vol. iv. p. 60) has described 

 with mach surprise, concretionary balls, with concentric divisions, 

 composed of partially vitreous feldspar, hornblende, and game s, 

 included within great veins of gneiss, which cut across the mica- 

 slate near Venezuela. 



