152 ORIGIN AND DEVELOPMENT OE ORE-DEPOSITS. 



A marked feature of this lode is the fact that numerous 

 quite narrow cross-veins cut across the ore-shoots and heave 

 them, or even abruj)tly terminate them, as, in the absence of 

 extensive explorations, would seem to be the case. This lode 

 has evidently been most imperfectly opened up, partly on account 

 of its very size — necessitating large capital to properly work 

 it — partly because of the very fluctuating character of the 

 demand for iron ore. Mr. Smyth's estimate of the total output 

 of iron ore up to 1880 was "something more than 150,000 tons," 

 but this is based («) on his estimate of the extent of the workings 

 in 1858, and {b) on the quantities recorded in Mr. Hunt's 

 Mineral Statistics. As to the first part I can say nothing, but 

 as to the second, it must be remembered that Mr. Hunt's figures 

 were obtained by voluntary assistance only, and in the case of 

 iron ore were always known to be defective. My own estimate* 

 was that 200,000 tons had been extracted up to that period. 

 Since then the output has been small, probably not more in all 

 than 10,000 tons. 



Of blende it is hard to say how much has been raised, 

 though the output in the case of Great Betallack has been 

 occasionally as much as 500, and in Duchy Peru 900 tons per 

 month ; on the whole it is not likely that the lode has yielded 

 in all less than 20,000 tons of blende, besides small quantities 

 of rich silver-lead and copper. These are small quantities for 

 so large a lode, and in fact great as the lode is, most miners 

 would rather look upon it as the great gozzan indicator of some 

 exceedingly rich copper vein existing at a greater depth than 

 as a lode valuable in itself for either iron or blende. 



(d) Special characters of lodes. The Dolcoath main lode and the 

 Perran iron lode afford illustrations of most of the characteristic 

 phenomena of the West of England fissure-veins, such as fissures 

 traversing indiscriminately or passing at times between different 

 kinds of rock, with their intersections and heaves by caunters 

 or cross-courses ; good and bad directions ; rich and poor parts ; 

 contact deposits ; gozzans and pseudomorphs; capels and flucans ; 

 breccias and concretionary structures ; combed structures and 



*Made m 1S73, when I was consulting engineer to the company then working, 

 ^nd so had opportunities of knowing the extent of the excarations, 



