ORIGIN AMD DEVELOPMENT OF ORE-DEPOSITS. 139 



2. The mean directions of cross-veins (cross-courses, flucans, 

 guides, traverses, &c., mostly non-metalliferous) is in the 



Most of these directions correspond to notable joint systems 

 in their respective districts, and many are at right angles or 

 nearly so to other notable joint or vein-systems. Although they 

 rarely contain ores of tin and copper, many have yielded 

 considerable quantities of iron ores, and in many more, valuable 

 local deposits of silver, cobalt, nickel, bismuth, uranium, and 

 other rare ores have occurred. In a few instances — as at N. 

 Poltiraore in Devon, Wheal Sparnon near Eedruth, and Woolf's 

 cross-course in Breage, spangles of gold have been met with. 



3. All the veins, whether metalliferous or not are apt to 

 vary considerably in inclination (underlie), yet it may be stated 

 in general terms that the cross-courses whether quartzes e or 

 yielding ores of iron or lead are steeper than the copper-veins, 



given tlie bearing of nearly all the lodes which he inspected. He however took 

 only the general hearing of the lode from one end of the mine to the other, 

 overlooking the variations between the productive and unproductive parts. By 

 this omission he not only lost a fine opportunity of accumulating many important 

 facts, but the whole subject of bearings by his mode of statement has a direct 

 tendency to mislead. Taking his report as a guide, the bearings would be no 

 indication whatever of productiveness or otherwise ; his rich lodes as well as poor 

 being found under almost every variation of direction. In reference to the 

 productive parts of lodes there is no such confusion, — order is all but universal — 

 exceptions if any, are rare indeed, and then of limited extent." (Chas. Thomas, 

 Remarks on the Geology of Cornwall, &c. Lecture 2, 1859). 



It is I hope needless for me to say that I do not call attention to this 

 criticism by a very eminent practical authority with any idea of diminishing 

 the lustre of our former President's labours— and after all the mean direction of 

 a lode as a whole is a matter of scientific importance ; but I would take this 

 opportunity to point out how verj important is this question of the bearing of 

 "rich parts" in a lode, and to urge practical men who alone can make the 

 numerous necessary observations to do so on all possible occasions. 



*Ibid, XXVIII. 



