Ch. X.] GENERAL REMARKS ON THE PRIMARY ROCKS* 193 



CHAPTER X. 



GENERAL REMARKS ON THE PRIMARY ROCKS. 



Recapitulation of the principal facts detailed in the preceding chapters. Com- 

 position of the granitic rocks. Each granitic formation characterised by 

 peculiar series of granite dependent on the nature of the accessory mineral. 



This mineral subject to transitions accompanied by corresponding 

 changes in the series. The different kinds of granitic rocks variously as- 

 sociated together, their disposition among the primary schists the nature 

 of this connection. Masses of granite whether large or small insulated or 

 interstratified with slates are not of a different nature. General remarks 

 on the primary schists their composition modes of union - and frequent 

 passage into each other. No fixed order of succession. Their nature 

 illustrated by a series, commencing with micaceous gneiss. The strata of 

 each member of the schistose group composed of slaty and compact varieties 



the latter pass into granitic rocks. This group in each primary district 

 characterised by the same minerals as the adjacent granite. Remarks on the 

 apparent fragmentary composition of some primary rocks, and on the ana- 

 logy between rock and mineral veins. 



IN the preceding chapters we have attempted, by detailed 

 accounts of the primary rocks of Cornwall, and by copious 

 extracts from the published descriptions of those of other 

 countries, to concentrate our information on this department 

 of the science, in order to prove that these rocks, wherever 

 they occur, resemble each other in the following respects: 

 they are composed of crystalline minerals, which, if not always 

 the same, are the equivalents of and capable of mutual transi- 

 tions into each other, and are subject to similar modes of 

 aggregation ; they also exhibit the same varieties of structure ; 

 and though in different districts, they present some diversity 

 in their aspect ; yet the manner in which the individuals of 

 each formation are associated together, perfectly corresponds. 

 It may be observed that this is not disputed, and that the 

 science of geology must not be studied within such narrow 

 limits; its object being not only a knowledge of each group of 



