424 Bahia, Brazil, part n. 



sequently to the breaking up of the dikes, 1 these latter 

 also having- been at the same time bent and softened. 



I must here take the opportunity of premising, 

 that by the term cleavage, I imply those planes of 

 division which render a rock, appearing to the eye 

 quite or nearly homogeneous, fissile. By the term folia- 

 tion, I refer to the layers or plates of different minera- 

 logical nature of which most met amorphic schists are 

 composed; there are, also, often included in such 

 masses, alternating, homogeneous, fissile layers or folia, 

 and in this case the rock is both foliated and has a 

 cleavage. By stratification, as applied to these forma- 

 tions, I mean those alternate, parallel, large masses of 

 different composition, which are themselves frequently 

 either foliated or fissile, — such as the alternating so- 

 called strata of mica-slate, gneiss, glossy clay-slate, and 

 marble. 



The folia of the gneiss within a few miles round 

 Bahia generally strike irregularly, and are often cur- 

 vilinear, dipping in all directions at various angles : 

 but where best defined, they extended most frequently 

 in a NE. by N. (or East 50° N.) and SW. by S. line, 

 corresponding nearly with the coast-line northwards 

 of the bay. I may add that Mr. Gardner 2 found in 

 several parts of the province of Ceara, which lies 

 between 400 and 500 miles north of Bahia, gneiss with 

 the folia extending E. 45° N. ; and in Guyana, accord- 

 ing to Sir R. Schomburgk, the same rock strikes E. 

 57° N. Again, Humboldt describes the gneiss-granite 

 over an immense area in Venezuela and even in Colombia, 

 as striking E. 50° N., and dipping to the NW. at an 



1 Professor Hitchcock ( c Geolog. of Massachusetts,' vol. ii. p. 673) 

 gives a closely similar case of a greenstone dike in syenite. 



- ' Geological Section of the Brit. Assoc' 1840. For Sir E. Schora- 

 burgk's observations, see ' Geograph. Journal,' 1842, p. 190. See 

 also Humboldt's discussion on Loxodrism in the ■ Personal Narrative.' 



