348 ON THE APPARENT DISLOCATIONS [Ch. XV. 



united with small and variegated portions of mica, shorl, or 

 hornblende, which are commonly equably diffused, imparting 

 colour to the slates ; and the compact felspar, since it con- 

 tains more silica than crystallised felspar, may be looked 

 on as an union of felspar and quartz. On this view, 

 both the granite and the slate have a similar composition, 

 differing from each other only in the proportions and in the 

 mode in which their constituents are combined, so that it 

 matters not whether the strata be gneiss or clay-slate in 

 contact with the granite ; it is equally easy to conceive these 

 various appearances to have arisen from the peculiar arrange- 

 ment of the constituent parts during combination. Let us 

 turn to the various felspathic rocks which exhibit light and 

 dark-coloured stripes, and these will often be found to display 

 the most intricate flexures and wavings ; and also sometimes 

 the light, and at others the dark parts, will be seen ramifying 

 and intersecting each other precisely in the same manner as 

 the granite and the slate ; and in the variegated marbles and 

 serpentines appearances somewhat similar may also be ob- 

 served ; and yet in none of these cases can it be supposed that 

 the veins and the bases have had a distinct origin. 



It is true that in these examples the rocks are of a more 

 simple composition, and therefore we do not find such great 

 contrasts as in the associated granites and slates; but this 

 cannot be a serious objection, since we not only find the 

 different kinds of granite in a state of union equally abrupt, 

 and also the various crystalline slates similarly circumstanced ; 

 but in the middle of a block of granite, far removed from the 

 schistose group, the constituents are oftentimes so arranged, 

 as not only to resemble angular portions of hornblende-rock, 

 shorl-rock, and porphyries, but also of gneiss, mica-slate, 

 and felspar-schists. Are we not taught by this, that what has 

 been produced on a small scale may have happened over 

 more extensive tracts. These small rays of light, however, 

 do not alone illuminate this interesting page of nature, but 

 others, gradually increasing in splendour, conduct us step by 



