Ch. IX.] VEINS IN PRIMARY ROCKS. 181 



throw out branches and fibres in every direction; and by 

 which the ends of a curve are sometimes connected. In 

 Polgooth, not only the veins, but the courses of porphyry, are 

 similarly curved; and that too on the line of their dip, as 

 well as on that of their lateral extension. According to 

 Mr. Kenwood's survey, this is of very general occurrence in 

 the veins of Cornwall; and he has obligingly furnished me 

 with the following illustrative example, from Huel Jewel mine 

 (near St. Day), which, below the adit, is entirely situated in 

 granite; and has afforded considerable quantities of the 

 black, grey, and yellow sulphurets of copper, but very little 

 tin ore. 



Fig. 17. 



60 fathoms to an inch. 70 fms. level. 



I 



- 70/m.v 



Huel Jewel Mine. (Bird's-eye View.) 



" The continuous lines denote the direction of the lode at 

 various levels : so that, if the dip of the lode were constant, 

 all the lines would have been parallel and equidistant, since 

 the successive levels are ten fathoms below each other. In 

 fact, the lode is as curved in its descent as in its course, and 

 thence the irregular appearances which it presents at each 

 level. The deviation from parallelism with the lode at the 

 adit level gives the variation of the dip at various depths ; it 

 is, however, always towards the north. The two series of 

 dotted lines denote two flucans (or friable, earthy veins, 

 having a more northerly direction than the regular E. and 

 W. metalliferous veins) ; and the distances between their 

 respective parts denote the variable quantity of their dip." 

 The phenomena of intersection which these flucans exhibit, 

 will be referred to hereafter. 



N 3 



