Ch, II.] DEFINITION OF THE TERM PRIMARY. 



CHAPTER II. 



DESCRIPTION OF THE GRANITIC ROCKS OF CORNWALL. 



Definition of the term primary as here employed. General aspect of primary 

 districts. The present nomenclature of the primary rocks defective. The 

 ternary compound of felspar, quartz, and mica, the type of granitic form- 

 ations : its varieties. Excess of felspar, and the accession of shorl, the cha- 

 racteristics of the granitic formation of Cornwall. The different kinds of 

 Cornish granite : shorl-rock, protogine, eurite, felsparite, and the quartzose 

 varieties of these rocks, or quartz-rock. These granitic rocks associated 

 together, as alternating beds, as irregular-imbedded patches or masses, as 

 veins, as elvans or dykes. 



BEFORE proceeding to describe the various primary form- 

 ations, it is desirable to define in what sense the word 

 primary is here employed; and this is the more necessary, 

 since it has not only fallen into disrepute both with foreign 

 and British geologists, but attempts have been lately made 

 to erase it altogether from the nomenclature, as conveying an 

 idea incompatible with the prevailing theory. 



The term primary, in its original acceptation, is certainly 

 very objectionable, inasmuch as it has a theoretical signi- 

 fication, which ought to be avoided in every classification: 

 but the word hypogene, by which Lyell has proposed that it 

 shall be superseded, is liable to the same objection ; and the 

 term crystalline schists, advanced by Boue, though free from 

 this defect, is not more happy, because several igneous and 

 sedimentary rocks have a similar characteristic. 



For these reasons we have continued to use the word 

 primary ; but, at the same time, regret the want of such a 

 term as would be generally applicable to rocks of this nature 

 without implying any hypothesis. In the mean time, how- 

 ever, it is proposed, in the following pages, to consider as 

 primary rocks the various kinds of granite, and all those 



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