36 DESCRIPTION OF THE PRIMARY fCh. IV. 



CHAPTER IV. 



DESCRIPTION OF THE PTIIMARY SCHISTOSE GROUP OF 

 CORNWALL. 



The division of the primary rocks into stratified and unstratified objectionable. 

 Proposed to divide them into granitic and schistose groups, only an artificial 

 arrangement, to facilitate description. Primary slates enumerated. Schistose 

 group of Cornwall. Consists of two series, the porphyritic and the calcareous. 

 Definition of these series. The slates next the granite variously named 

 by Geologists. They are of a peculiar nature. Of two kinds, one 

 bounding the eastern, the other the western granite. They pass into other 

 kinds of slate. The nature of this transition. Greenstone, Actynolite- 

 rock, Chlorite-rock, and the Magncsian rocks, Talc-schist, Serpentine, and 

 Euphotide, described. Remarks on the quartzose varieties of all these 

 rocks, commonly called quartz-rock. Nature and position of the granitic 

 rocks or elvans, in the schistose group of Cornwall. 



THE primary rocks have been divided into stratified and un- 

 stratified; the latter comprising the various granitic rocks, 

 which generally occur in large insulated clusters, and have a 

 compact and massive structure ; the former denoting those 

 non-fossiliferous rocks which surround, and are intimately 

 connected with the granite, and are very commonly distin- 

 guished by a slaty or schistose texture. 



It will be found, however, that this division is perfectly 

 arbitrary; for both stratified and unstratified rocks are so 

 intermixed in their associations, that it is sometimes impossible 

 to decide to which of these classes a rock, under examination, 

 belongs : in order, therefore, in some measure, to avoid this 

 confusion, the primary rocks will, in the following pages, be 

 supposed to consist of granitic and schistose groups; only 

 understanding by this division, that in the one granites, and 

 in the other slates predominate ; and it must not be forgotten 

 that this is an artificial, not a natural arrangement, merely to 

 facilitate description. 



