248 AN ENQUIRY INTO THE [Ch. XII. 



the immediate vicinity of the granite. It is not necessary to 

 stop in this place to enquire how it is that these and the pri- 

 mary slates can seldom be distinguished from each other, 

 except by some sparingly scattered and obscure organic 

 remains, so insensibly do they pass into each other ; nor to 

 investigate the reason why the composition of these transition 

 slates so seldom exhibits marks of their having originated 

 from the detritus and debris of decomposed rocks : but must 

 at present rest satisfied with the fact that both these orders of 

 slates do possess a similar structure. 



Mr. John Phillips, in his description of the schistose rocks 

 between the rivers Lune and Wharfe, has frequently noticed 

 this structure. Some difference of opinion may be enter- 

 tained as to the precise geological era to which each of the 

 three divisions of slate composing this district belongs : but 

 this is, in the present question, of little consequence ; it is 

 only extending the subject of comparison from the primary 

 to the carboniferous series. " Few subjects," says this intel- 

 ligent geologist *, " are involved in greater difficulty than the 

 question of the stratification of slate. We see this rock 

 divisible into layers, and sometimes observe these layers 

 alternately of a finer or coarser texture, appearances which in 

 shale would be deemed very satisfactory evidence of the 

 laminae of deposition ; but the generally vertical direction of 

 the layers or planes of cleavage, and the numerous geometri- 

 cally intersecting joints, leave much doubt in the case of 

 slate. This difficulty is not lessened by the fact that, in 

 many kinds of slate, there are really two cleavages or sets of 

 laminae, made evident by particular circumstances of wea- 

 thering, though generally only one, which may be called the 

 true cleavage, is practicable by blows. The oblique laminae 

 of false cleavage are generally regular and parallel to each 

 other, and intersect the planes of true cleavage at certain 

 angles, constant for the same quarry." Again, " from finding 



* Geol. Trans., New Series, vol. iii. p. 16. 



