88 CRANITE. 



bable that there has been granite, or an analogous 

 substance, prior to all strata, and the original source 

 of the whole. That very granite may be visible; but 

 we cannot as yet distinguish it from the many succes- 

 sive ones which have acted in the elevations of the 

 strata. 



With its mineralogical resemblance to the trap 

 family, there are many striking points of correspond- 

 ence in their geological disposition, and in their rela- 

 tions to the secondary rocks. But I need not re- 

 examine a subject formerly discussed under a general 

 view : though some of the particulars will re-appear 

 in this and the succeeding chapter. But as granite 

 has been said to be distinguishable under certain ceras 

 of formation, leading to the terms of primary and se- 

 condary, of older and of newer, I must enquire of that 

 matter. The ordinary criterion of such ages, thus 

 produced, is fallacious ; though it has certainly been 

 formed at many different periods. Among stratified 

 rocks, the criterion of superiority will, in general, 

 mark the latest. But between an unstratified in- 

 truding rock, and a stratified one, there can be no 

 such assignable relation ; since the former may be 

 equally in contact with the strata of various ages, if it 

 be posterior to the whole. Though it should be pos- 

 terior to some only in a series, we cannot even then 

 know the relative period of its formation ; as it might 

 not have come into contact with every stratum of the 

 mass into which it has intruded, even though of later 

 origin than the whole. There is no criterion then of 

 this nature ; but there is one by which the relative 

 aeras, at least, of two masses of granite can be deter- 

 mined. That is the passage of veins from one mass 

 into another : a fact, of which the value has, from hy- 

 pothetical views, been generally overlooked. The 



