232 AN ENQUIRY INTO THE [Ch. XII 



rock is of igneous or aqueous origin : the student, for whose 

 assistance definitions are more peculiarly intended, can rarely 

 make such a discrimination, and it must therefore be pro- 

 nounced to be defective. 



It is very true that it is well understood what is meant by 

 the word stratum, though it is so difficult to embody the idea 

 in correct language : but this very circumstance should induce 

 us to suspect the propriety of employing such a term. So 

 far, however, from this being the case, in defiance as it were 

 of the indefinite nature of the term stratum, all rocks what- 

 soever are, according to the modern classification, divided into 

 the stratified and unstratified. 



If this statement be correct, it furnishes a curious subject 

 for enquiry, how a system, apparently so illogical, could have 

 been universally received ? And it may diminish the surprise 

 that otherwise might be felt, at our attempting to maintain so 

 heterodox an opinion, as that the primary schistose rocks are 

 not stratified. This, of course, can only be indirectly proved, 

 since the term stratum has no precise meaning, by showing 

 that if these rocks are stratified, then granite, porphyry, and 

 similar rocks are likewise arranged in strata ; but if the latter 

 are unstratified, so are the former, because they do not possess 

 any characters indicative of a distinct origin ; both the granitic 

 rocks and the primary slates being so intimately connected 

 together in composition and structure, that the latter appear to 

 be only mechanical modifications of the crystalline masses with 

 which they are associated. 



The opinion that gneiss and mica-slate are only micaceous 

 and argillaceous sandstones, altered by the action of heat ; 

 and that quartz-rock and granular marbles are but siliceous 

 sandstone and secondary limestone, which have undergone a 

 similar change, is certainly in favour of the primary slates 

 being stratified rocks ; but, according to one version of the 

 Plutonic theory, and the one least easily controverted, even 

 some granites are altered stratified rocks ; and, therefore, on 

 this view, granite and its accompanying slates only differ from 



