1 68 Cape of Good Hope. ?aet i. 



theory, of granite having been injected whilst liquefied; 

 but if we reflect on the probable state of the lower 

 surface of a laminated mass, like clay-slate, after having 

 been violently arched by a body of molten granite, we 

 may conclude that it would be full of fissures parallel 

 to the planes of cleavage; and that these would be 

 filled with granite, so that wherever the fissures were 

 close to each other, mere parting layers or wedges of 

 the slate would depend into the granite. Should, 

 therefore, the whole body of rock afterwards become 

 worn down and denuded, the lower ends of these de- 

 pendent masses or wedges of slate would be left quite 

 isolated in the granite ; yet they would retain their 

 proper lines of cleavage, from having been united, 

 whilst the granite was fluid, with a continuous covering 

 of clay-slate. 



Following, in company with Dr. A. Smith, the line 

 of junction between the granite and the slate, as it 

 stretched inland, in a SE. direction, we came to a 

 place, where the slate was converted into a fine-grained, 

 perfectly characterised gneiss, composed of yellowish- 

 brown granular feldspar, of abundant black brilliant 

 mica, and of few and thin laminae of quartz. From 

 the abundance of the mica in this gneiss, compared 

 with the small quantity and excessively minute scales, 

 in which it exists in the glossy clay-slate, we must 

 conclude, that it has been here formed by the meta- 

 morphic action — a circumstance doubted, under nearly 

 similar circumstances, by some authors. The laminae 

 of the clay-slate are straight ; and it was interesting to 

 observe, that as they assumed the character of gneiss, 

 they became undulatory with some of the smaller 

 flexures angular, like the laminae of many true meta- 

 morphic schists. 



Sandstone formation. — This formation makes the 



