CRIFFEL DISTRICT. 140 



while in another there is so complete an intermixture, that 

 it is almost impossible to tell where the one rock begins, and 

 where the other ends. The size of the veins bears no rela- 

 tion to the degree of intermixture of them with the grey- 

 wacke ; on the contrary, a very large vein may pass into 

 the rock, or it may not, or a small vein, in size perhaps not 

 exceeding three or four lines, may be completely commingled 

 with the greywacke which it traverses, or may have a de- 

 terminate outline. 



In its mineralogical structure, the rock which forms the 

 veins frequently differs from that which constitutes the larger 

 masses. The several components, the quartz, felspar, and 

 mica, or the felspar, quartz, and hornblende, become inti- 

 mately and obscurely intermixed with one another ; and in 

 many places the veins are composed of an intermixture of 

 quartz and felspar, which is sometimes so perfect that the 

 veins appear to be composed of a very compact felspar. 



The appearances which the greywacke exhibits when 

 in the neighbourhood of the granite and syenite, are ex- 

 pressive of indurating or altering causes : in every instance 

 it becomes compact, the slaty varieties passing into a spe- 

 cies of felspar, not unlike some clinkstones. In both the 

 granite and the greywacke, shifts may in some places be 

 observed ; the sides of these shifts, however, are so inti- 

 mately connected as to render it highly probable that they 

 have taken place before the granite was in a perfectly con- 

 solidated state. In regard to the stratification of the grey- 

 wacke, it varies in regularity ; sometimes the rock being per- 

 fectly amorphous, while in other places it exhibits a more 

 or less bedded structure, the strata then dipping to the S. 

 S. E. at angles between 30° and 70°, and resting upon the 

 principal mass of granite and syenite. In one or two places 

 layers of quartz occur in the greywacke ; in every instance, 

 however, these are to be observed only near the granite ; fi„ 



