ORIGIN AND DEVELOPMENT OF ORE DEPOSITS. 139 



evident in regions where the rocks are of such a nature as to 

 retain some notable degree of plasticity, but "drag" is rarely 

 entirely absent, except in very solid and massive rocks. 



In the lodes of Cornwall the "drag" is generally taken 

 into account by the experienced miner who is in search of a lost 

 lode, a species of instinctive perception guiding and influencing 

 him, even when he professes not to believe in earth movements 

 at all. A good illustration occurred some years since at East 

 Carn Brea Mine, which is illustrated in fig. 11. A number of 

 small elvan courses occur in one part, parallel, or nearly so, to 

 the lamination of the killas, which is here traversed by many 

 lodes parallel, or nearly so, in strike and dip. At some distance 

 from the lodes the strata are more or less horizontal, but on 

 approaching a lode they become considerably inclined, being 

 tilted up on the hanging-wall side and bent down on the foot- 

 wall. " The hanging side of the lode is always the lower, as if 

 it had slipped down. The direction of the movement of strata 

 is clearly proved, by the slicken sides, to have been up and down, 

 and the courses of elvan shew the extent of the dislocation."*' 



Slichensides and flucans. In the preceding paragraph refer- 

 ence has been made to slickensides as indicating an up and down 

 motion in the fissure. The peculiar shining striations so-named 

 are familiar to miners in all countries, and are rarely absent 

 from true fissure lodes. That the rubbing has been continued for 

 some considerable time is indicated by the polished character of 

 the surfaces ; even when very hard the scratches are sometimes 

 very deep ; they often succeed each other, as if the fissure had 

 been partially filled up and the motion renewed ; and they are 

 frequently accompanied by considerable quantities of the adhe- 

 sive clay, known to the miners as "flucan." This flucan is 

 regarded as a good sign by most miners, especially for copper. 

 So, indeed, it is, not because of any particular affinity between 

 clay and metallic minerals — in fact flucan is as abundant or 

 perhaps more so in the barren cross-courses as in the productive 

 lodes — but simply because it indicates such a long-continued 

 opening of the channels, through which the metallic solutions 

 have made their way, as would give time for their deposition in 



*S. Bawden, Rep. Miner's Assoc, of Cornwall and Devon, 1866, p. 30. 



