166 Mr Hen wood on the Phenomena of 



or vein stones from the general mass j these, it is evident, could 

 not have existed as fissures for a moment." 



I select Mr Hopkin's excellent results as tending to bring 

 the theory of fissures within the dominion of exact science ; ra- 

 ther than the equally ingenious opinions of some other gentle- 

 men, not based on such unexceptionable investigations as his 

 mathematics. 



We now approach the last division of our subject, the Jilting 

 of the fissures^ and here we again meet Werner, Hutton, Pro- 

 fessor Sedgwick, and Mr Fox. 



It has been already seen that Werner thought veins were 

 filled from above ; his proofs may be all comprised in the oc- 

 currence of masses of the contiguous rocks, and of round stones 

 in the veins. It has been seen that these contained masses al- 

 ways resemble the rock at that spot in contact with the vein and 

 not of superior rocks. In this county the well known Relistian 

 lode has been often quoted. But whoever will examine the 

 walls of this vein, will see that a very similar structure prevails 

 in the rock itself. Nothing is much more common than a sphe- 

 roidal concretionary form ; in the elvans it is frequently very 

 well shewn on decomposition. I have seen some of the best 

 cases at Tresamble, in Gwennap. In the granite, too, we ob- 

 serve similar nodular concretions," of dark colour, and fine grain- 

 ed, and which, " indeed, if sufficiently abundant to predominate 

 over the containing rock, would exhibit a conglomerated struc- 

 ture. In the globular granite of Corsica, however, we have a 

 noted example, in which the constituent minerals are arranged 

 around certain centres, in concentric laminae." We see there- 

 fore that rock masses, which, by the common consent of geolo- 

 gists of all opinions, are attributed to no derivative origin, possess 

 the same conglomerated structure. I know of but one case in 

 this county in which I should consider the filling up of a vein 

 to have been mechanical, this is the Badger lode, in the Herland 

 Mines, and where we have rounded and angular pieces of gra- 

 nite, slate and elvan, imbedded in the same felspar clay. In 

 the secondary rocks, however, which Werner studied, it is not 

 uncommon to find even organic remains in the veins ; that these 

 are of posterior date, admits, I think, of no doubt. 



The theories of injection and sublimation appear both to hav e 



