556 Remarks on Dr. Boast's Primary Geology. 



by mineral transitions, and vary in composition as the nature of the 

 rock changes ; they are not straight, but are curved both in their 

 course and dip ; their sides or walls are only distinct from the rock 

 when the seams or joints are developed by decomposition, and are 

 always partially confounded with the rock by a perfect intermixture 

 or transition ; they intersect each other both in length and depth, 

 and in the larger veins those series which run in the same direction 

 are generally affected by the others in a similar manner ; but this 

 is not invariably the case : their intersections are very frequently 

 attended by alterations in the course of the disconnected veins, but 

 the amounts of these apparent movements, in an extensive series, are 

 very various, even in the case of a single intervening vein." 



In the 10th Chapter, the author sums up the inferences he 

 draws from the results of his investigation of the phenomena 

 of the primary formations of Cornwall, and its comparison 

 with the description of that of other countries : these remarks 

 may be abridged as follows : 



\st. That there is always a similarity of mineral composition 

 between the granitic rocks and the adjacent primary schists, 

 with which they are associated. 



2nd. That the same brecciated structure or apparent 

 origin from the conglomeration of fragments occurs both in 

 the schistose and granitic primary rocks, and if allowed to be 

 an evidence of derivative origin in the one case, so must it 

 also be allowed in the other. 



3rd. That the granitic and mineral veins of Cornwall, 

 gradually pass into the rocks they traverse, and both present 

 the same appearance of heaves, slides, and similar phenomena, 

 commonly referred to motion, when veins of the same or of a 

 different class interfere with each other. 



4th. That the origin of both the schistose and granitic rocks 

 is the same. 



bth. That parts of the schistose formation present by in- 

 sensible graduation a perfect granitic structure. 



6th. That the primary schists are not stratified, or that the 

 granitic formations are as much stratified as the schistose. 



