154 Mr Kenwood on the Phenomena of 



adds, "all true veins were originally and of necessity rents open 

 in their upper part, which have been afterwards filled up from 

 above ;" he continues, "the vein, after its first formation^ may 

 have been again opened up," and he considers the parallel lay- 

 ers, of which veins sometimes consist, as the deposites after such 

 successive openings.* 



Professor Sedgwick says, " In all the crystalline granitoid 

 rocks of Cornwall, there are also many masses and veins of se- 

 gregation. Such are the great and contemporaneous masses 

 and veins of schorl-rock ; and some of these are metalliferous. 

 The decomposing granite of St Austell Moor is traversed, and 

 sometimes entirely made up of innumerable veins of this de- 

 scription. Upon these lines of schorl-rock there is often ag- 

 gregated a certain quantity of oxide of tin, which diffuses itself 

 laterally into the substance of the contiguous granite." After 

 having examined it, he " left it with the conviction that several 

 of the neighbouring tin- works were not opened upon true lodes, 

 but upon veins of segregation." 



In my own opinion, however, the best description of the 

 veins of this county (and of these alone unless the contrary, he 

 expressly said, I beg to be understood as speaking) is given by 

 Dr Boase, in his valuable memoir on the geology of Cornwall, 

 in the fourth volume of the Cornwall Geological Society^ Trans- 

 actions. I concur most fully in every one of his statements ; 

 and the nature of the relations between the veins and their con- 

 taining rocks, are so well described, that were I to attempt one 

 of my own, it would be but a repetition of the same ideas. 



" The veins of Cornwall have no determinate size, being 

 sometimes very narrow, or exceeding several fathoms in width, 

 extending sometimes to a great length and depth, or terminat- 

 ing after a short course in either direction. As regards their 

 form, they are occasionally, though rarely, contained within 

 parallel and regularly inclined sides or walls ; but are continu- 

 ally varying in width, both on the line of their course and of 

 their inclination, partaking often of the same undulating, and 

 even curved, form of the rocks which they traverse ; moreover, 

 they are accompanied on either side by innumerable branches, 



Vide Dr Anderson's translation of Werner's classical work on Veins, 8vo, 

 pp. 259. Edinburgh, 1809. 



