140 



ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



the copper-veins steeper than the tin-veins, and all the 

 metalliferous veins steeper than the clayey slides. Perhaps the 

 averages may be stated as under : 



Cross-courses, &c., 80° from the horizontal. 

 Copper- veins, 70° ,, ,, 



Tin- veins, 60° ,, ,, 



Slides, 45° „ „ 



In the case of the tin-lodes there are, however, many very 

 notable exceptions to the average stated above. Thus, the great 

 Flat lode to the south of Carn Brea Hill, the lode at Wheal 

 Kitty, Wheal Jane pyritous lodes, and many others have 

 inclinations of less than 40° from the horizontal. 



4. Of the mean width of the lodes, Mr. Henwood says :* 



Those which yield (or have yielded) the ores of tin 



and copper, average 

 Those which yield tin ore only . . 

 Those which yield copper ore only 

 Lodes generally in granite 



,, in slate . . 



„ at less than 100 fathoms deep. 



,, at more than ,, 



Cross-courses in granite . . 



4-7 feet 



3-0 

 2-9 

 3-1 

 3-7 

 3-9 

 3-3 

 4-9 

 3-5 

 ,, at less than 100 fathoms . . 4-0 



„ at more ,, . . 4.4 



It thus appears (a) that tin lodes are wider than copper 

 lodes, which is what we might expect from the common occurrence 

 of workable tin capel and the rarity of copper capel. 



[b). Lodes of tin and copper are wider than those of either 

 separately, which also we might expect, because it would appear 

 in many cases at least that the copper has been deposited in a 

 re-opened fissure previously containing tin. 



(c) The lodes are narrower than the cross-courses: a reason 

 for this may be suggested hereafter. 



As to the mean width of lodes in depth — as compared with 

 their shallower portions — I would observe that the figures which 

 might now be obtained would probably differ considerably from 



* Ihid, pp. XV. xxviii. 



