Metalliferous Veins. 159 



ly; depending also on the nature of the rock they traverse* 

 Slides are often veins of clay only ; but they often also become 

 quartzose, and sometimes, as in some at St Agnes, they are 

 metalliferous. 



The directions or bearing of the greater number of metalli- 

 ferous veins in this county, are within a few degrees of magne- 

 tic east and west ; of the slides nearly the same ; the elvans 

 are generally rather more to the south of west and north of east 

 than the lodes ; whilst the cross-courses andjlucans bear within 

 a few degrees of north and south. There is, however, a metal- 

 liferous series of veins, the contra or counter lodes, which have 

 ajdirection of about north-west and south-east ; whilst the lodes 

 of the parish of Saint Just are about north and south, and the 

 cross-courses or guides about north-east and south-west. 



It is a general fact, that there are seldom or never in the 

 same district two metalliferous series at right angles to each 

 other. 



The rocks, too, are traversed by lines of symmetrical struc- 

 ture, the (queres), which have a kind of rough approximation 

 to the directions of the veins ; one of the principal sets bearing 

 about north and south, whilst a second stands about east and 

 west, and a third is nearly north-west and south-east. 



This coincidence, so far as I know, was first alluded to by 

 Dr Boase, who says, " it has often struck me that the large 

 veins correspond with the seams of the layers of rocks, and the 

 smaller* ones with those of the component blocks and laminae of 

 these layers ; I have repeatedly detected this coincidence." The 

 subject has recently attracted the attention of Professor Phil- 

 lips, Professor Sedgwick, and Mr Hopkins, and all these excel- 

 lent observers have given details of great value. 



Whether these be synchronous with the rocks themselves, or 

 of posterior origin, has lately been discussed by Dr Boase and 

 Mr Hopkins ; the former maintaining the affirmative, the lat- 

 ter the reverse. It is well known that these lines traverse, of- 

 ten without interruption, the granite, slate, elvans, and veins; 

 although sometimes the same want of coincidence, which, in the 

 case of Iode8 9 is called a heave, is observed. It is, I think, clear 

 that, if produced in the slate by any dislocating elevation, the 

 lodes must have been contemporaneous with that movement, if 



