342 A Geognostkal Sketch of [Nov. 



the great importance attached to the lime-stone beds in this country. 

 A very great proportion of the lead ore has been extracted from the 

 Great Lhrie'-^stone. Every mine I visited situated in the Great Lime- 

 stone was exceedingly rich. This was the case at Crossfell, Allon- 

 heads, and some of the mines i:i Weardale. One of the richest 

 minis for many years was Rampgill, situated in a hill between 

 Ga; te and Nent Head. The vein run? east and west, and 



in the Great time-stone became of considerable width, and con- 

 Teat measure of pure galena. This mine is still consi- 

 dered as good, though it is now greatly inferior to what it once was. 

 ife substance with which these veins are filled is frequently 

 in called Cros I rnishes one of the most striking 

 It is a north and south vein, and passes along the east 

 Is it stands above the surface, it is very conspi- 

 duotJ I traced it for some miles. It is about a fathom wide, and 

 consists of pure white quartz. Here and there pieces of iron and 

 copper | and in it, especially near the hanks of a small 



rii ' which crosses it. A level was driven in here for some way, 

 in order to ascertain whether the quantity of copper was sufficient 

 to make it worth while to work the vein ; but the experiment was 

 not attended with success. 



Another mineral very common as a vein-stone in this county is 

 lime-stone. In many mines I saw a considerable mixture of clay 

 in the stuff brought up from the vein ; and hence am disposed to 

 consider clay as another substance with which these veins are occa- 

 sionally filled. Fluor spar is another common vein-stone, and 

 occurs more or less in almost all the veins that contain lead ore. In 

 W< ardale (that is to say, the mining district on the banks of the 

 YVea'.e) most of the veins that I examined were filled with fluor 

 spar and galena. 



Galena is the substance to which these veins owe their value. 

 Sometimes it constitutes a thin bed (if I can use the expression) in 

 the centre of the vein ; but more frequently it is irregularly dis- 

 persed through the vein-stone. The poverty or richness of a vein 

 always refers to ihe proportion of galena which it contains. Veins 

 are usually richest in lime-stone, and poorest in sand-stone and 

 slate-clav. They have been found to become the poorer the deeper 

 tksf Rre followed. Just the opposite of this is the case with the 

 copper-mines in Cornwall, which become more and more productive 

 the deeper down they are followed. 



The Huor spar is usually crystallized in cubes, and some of these 

 cubes are of ah enormous size. I have seen them four or five 

 inches a side, and probably they have occurred :-;till larger. At 

 present they ai much scarcer than they used to be. In some of the 

 mines (at / :ds, for example, where 1 saw very perfect 



exai \ hose vein-stones consist chiefly of a mixture of 



fluor spar and quartz, a .cry unaccountable circumstance has, been 

 noticed lat( ly. The fluor spur has in many places totally or partially 

 .ing a cubic cavity in the place which was formerly 

 occupied by t'.. crystal. In what manner this singular 



