of Northumberland and Durham. . 91 



The metallic veins which intersect the lower beds of this 

 section are always most productive, as they pass through 

 the limestone, and of the numerous beds of limestone that 

 called the Great limestone is by far the richest in ore. The 

 general direction of the principal veins is from east to west ; but 

 there are other veins which run from north to south, and inter- 

 sect the above nearly at right angles. These are called cross 

 courses. The first are called right running veins. The cross 

 courses sometimes produce ore at their junction with the north 

 and south veins, and at a little distance on each side of the latter. 

 A curious fact is stated by Mr. Forster, that most of the east and 

 west veins on Wear dale throw the strata on the north side or 

 cheek of the vein up, and the vein declines to the south ; but 

 most of the veins at Alston Moor and Allen Dale throw tlie 

 strata on the south side or cheek up, and the vein declines to the 

 north. The beds of rock in this mining field being composed 

 of different strata, calcareous, siliceous, and argillaceous ; it is 

 found that the nature of the rock affects' the contents of the vein. 

 In the calcareous the ore is most abundant; in the siliceous or 

 sandstone beds the veins are seldom very productive of ore, and 

 iti the argillaceous strata, or plate, ore is scarcely ever found m 

 th& vein. It is also to be noticed, that the vein hi passing the dif- 

 ferent beds becomes much narrower in tbe hard siliceous strata, 

 and is sometimes nearly closed as it passes through them, but it 

 again becomes wider in the limestone and plate. The inclina- 

 tion (or what is called the hade) of the vein is the greatest ia 

 passing through the soft stra,ta, but in the hard strata above or 

 below it takes its former inclination again, so as frequently to have 

 a kind of zigzag course as it descends. It is also particularly 

 deserving attention, that when the beds on one side of a vein ave 

 thrown up, and recks of a different kmd face each ottier, so that Oiie 

 side of the vein will have a wall of limestone and the other of sandr- 

 stone or plate, the vein is seldom, if ever, so rich in ore as wheo 

 both walls are of the same kind of rock,; on v, hieh account it is 

 found that the most productive veins are those where the rock on 

 either side has but a small throw up, and of course the walls or 

 cheeks of the veins (as they are called) are formed of the vsame 

 eti-atum on both sides. 



The almost invariable change in the quality or in the contents 

 of metallic veins, as they pass through different rocks, is, I cou- 

 ceive, a demonstrative proof of the fallacy of Werner's theory, 

 vwliich represents veins as open fissures filled with metallic solu- 

 tions from above, either by an aperture at the top or through 

 openings in the sides. Were veins filled in this manner, the qua- 

 lity of the rock could have little influence on the ore. Werner 

 i|uotos au instance at Kingsbergh in Norway, as if it were unique, 



of 



