Remarks on Dr. Boasts Primary Geology. 543 



" It prevents the student from taking practical lessons in the 

 book of nature, until he has completed the course of theoretical 

 instructions ; and then it too frequently happens, that he can only- 

 make his observations according to the prescribed rules, and under 

 a particular bias, prejudicial to impartial observations. " 



By theoretical Geologists, it is contended that the mineral 

 character of a rock is a subject of little importance, because it 

 does not afford the means of estimating the supposed age or 

 the time of its formation ; but without entering at any length 

 upon the discussion of such views, it will be seen at once 

 that in a descriptive science, it is by the mineral character 

 alone that a rock can be identified.* In advocating the ad- 

 vantages of a nomenclature depending upon geological rela- 

 tions, Humboldt is made to remark in the English translation 

 of his work on the e superposition of rocks/ page 8 : 



" Under the equator, as in the north of Europe, the beds of a real 

 transition syenite lose their hornblende without becoming another 

 rock." 



Now as a rock is a crystalline aggregation of several minerals, 

 and as its identity depends on the number, the proportion, 

 and the mode of aggregation of the component minerals ; it 

 is difficult to understand how it can be asserted, that a rock 

 is the same, when it is avowedly different. Dr. Macculloch 

 has, with his usual acumen, detailed and considered the 

 advantages and disadvantages of both the geological and 

 mineralogical methods, but the correctness of the following 

 remarks of our author will probably not be denied : 



* In descriptive science we ought not to exclude any characters, and it is in this 

 spirit we believe that geological enquiries are now conducted. It is true that in 

 primary rocks we have hardly any other than mineral characters to guide us. We 

 may remark, however, that some of the so-called primary rocks, even some of those 

 we believe described by Dr. Boase in the West of England, have by the more 

 recent enquiries of Sedgewick and De la Beche been found not to be so. We 

 allude particularly to certain slates of Devonshire, in which distinct and peculiar 

 fossil remains are now found, although they were previously regarded, we believe, 

 as primary. — Ed. 



