chap. xin. Cleavage and Foliation. . 463 



Venezuela, and indeed over a much larger space, gneiss, 

 granite, mica, and clay-slate, striking very uniformly 

 ISTE. and SW., and dipping at an angle of between 60° 

 and 70° to NW. : it would even appear from the facts 

 given in this chapter, that the metamorphic rocks 

 throughout the north-eastern part of S. America are 

 generally foliated within two points of NE. and SW. 

 Over the eastern parts of Banda Oriental, the foliation 

 strikes with a high inclination, very uniformly NNE. to 

 SSW., and over the western parts, in a W. by N. and 

 E. by S. line. For a space of 300 miles on the shores 

 of the Chonos and Chiloe Islands, we have seen that the 

 foliation seldom deviates more than a point of the com- 

 pass from a K 19° W. and S. 19° E. strike. As in the 

 case of cleavage, the angle of the dip in foliated rocks 

 is generally high but variable, and alternates from one 

 side of the line of strike to the other side, sometimes 

 being vertical : in the northern Chonos Islands, however, 

 the folia are inclined almost always to the west; in 

 nearly the same manner, the cleavage- laminae in 

 southern Tierra del Fuego certainly dip much more 

 frequently to SSW. than to the opposite point. In 

 eastern Banda Oriental, in parts of Brazil, and in some 

 other districts, the foliation runs in the same direction 

 with the mountain-ranges and adjoining coast-lines: 

 amongst the Chonos Islands, however, this coincidence 

 fails, and I have given my reasons for suspecting 

 that one granitic axis has burst through and tilted the 

 already inclined folia of mica-schist : in the case of 

 cleavage, 1 the coincidence between its strike and that 

 of the main stratification seems sometimes to fail. 

 Foliation and cleavage resemble each other in the planes 

 winding round concretions, and in becoming tortuous 



1 Cases are given by Mr. Jukes, in his ' Geology of Newfoundland,' 

 p. 130. 



