Ch. X1L] NATURE OF STRATIFICATION. 233 



each other in the degree m which the supposed lines of strati- 

 fication have escaped obliteration. But is this altered con- 

 dition of the primary slates infallibly demonstrated? We 

 think not: but this subject will be discussed under its ap- 

 pointed head : for the present we must confine our attention 

 to the mechanical arguments derived from the form and 

 structure of these rocks. 



" The propriety of the term stratified, as applied to the 

 primary slates," says Professor Lyell, " will not be ques- 

 tioned, when the rocks so designated are carefully compared 

 with strata known to result from aqueous deposition." * He 

 then proceeds to point out the analogies between these form- 

 ations, and states, that " if either of the primary slates be 

 examined, we find that it is made up of a succession of beds, 

 the planes of which are, to a certain extent, parallel to each 

 other, but which frequently deviate from parallelism in pre- 

 cisely the same manner as the sedimentary beds of all ages." 



This resemblance between the structure of the primary 

 and secondary slates is certainly correct ; but it is no less 

 true that the individual layers of which a mass of granite is 

 composed, exhibit the same appearances as those of the 

 stratified rocks. The parallelism of the layers or beds of 

 granite, is a point which, it is presumed, will be readily con- 

 ceded : indeed, it follows from the structure of this rock (as 

 already described), that the beds may be either horizontal or 

 perpendicular, when the granite is of the common type, or 

 variously inclined, according to its nature and composition ; 

 and, what is of great moment, the direction or strike of these 

 granitic beds is placed in a certain and determinate position, 

 which in Cornwall is parallel with the most frequent course 

 of the adjacent schistose rocks. This is no new statement ; 

 the same things have been remarked by many observers ; 

 but who, biassed perhaps by theoretical considerations, have 

 not given them that weight which they appear to merit. 



* Principles of Geology, vol. iii. p. 363. 



