1814.] Nor thunder land, Durham, &c. 3-41 



slate-clay whenever they are so hard as not lo be capable of being 

 wrought, except by blasting. All the specimens of whin shown 

 me belonged to one or other of these two rocks, and 1 saw no other 

 mineral except these to which the term was applied. 



The colour of the slate-clay varies a good deal in different beds. 

 Sometimes it is black, bituminous, and breaks spontaneously into 

 thin slaty fragments. This variety, which approaches the nature of 

 shale, is called shiver by the miners. The most common colours 

 of the slate-clay are blue, brown, and grey. 



4. The sand-stone beds amount to about 50. Many of them are 

 thin, scarcely exceeding a fathom; but there are some beds, espe- 

 cially near the bottom of the formation, nearly 18 fathoms thick. 

 This sand-stone is usually fine-grained, and has commonly a grey or 

 yellowish colour. It is distinguished among the miners by the name 

 of hazle, obviously from its colour. When the grains are uncom- 

 monly large, as is the case in some of the beds, it is called grit ; 

 and some beds, from the uses to which they are applied, have 

 received particular names, as mill-stone grit, grind-stone sill. The 

 word sill is the term applied in this country to a mineral led. One 

 of the most beautiful sand-stone beds is the one which constitutes 

 the summit of Crossfell. It is fine-grained, of a light grey colour, 

 pretty hard, and seems very well adapted for a building s'one. I 

 conceive it to be the sixth bed immediately below the Great Lime- 

 stone ; but I might easily be mistaken, as there was a considerable 

 interval between the place where the Great Lime-stone was exposed 

 and the summit of Crossfell; and this interval, being covered with 

 moss, could not be examined. 



5. This formation is intersected by a great variety of veins, most of 

 which are very well known, as they have been wrought as mines 

 for at least these 200 years. The oldest of these veins runs from 

 north to south ; but as they are the least numerous, and most 

 insignificant, they are called by the miners cross veins. In going 

 up the level from Alstone towards Nent Head, 1 had an opportunity 

 of seeing a variety of veins cross each other, and of ascertaining 

 that the north and south veins are always the oldest. IJut the most 

 numerous and important Bet of veins ate those that run east and 

 west. They are the newest ; but as they contain most of the lead 

 ore which has given importance to tl is district, they are considered 

 as the principal ones. These \eins differ very much in wideness ; 

 some are onlv a few inches wide, while others are several fathoms. 

 The width of the suite vein is found to vary in the different beds 

 through which it passes. It is apt to become narrow in passing 

 through the slate-clay beds, and to widen very much when it passes 

 through the lime-stone. Such a widening is called fiati by the 

 mi ers. [ saw a striking example of it at Alton heads mine. The 

 vein before it entered the Great Lime-stone was two or three feet 

 wide, and very poor of galena ; but on entering the Great Lime- 

 stone it suddenly swilled out to a width of twelve fathoms and 

 b came exceedingly rich in galena This increase of produce is 



id to be almost a constant attendant of this swelling out. licuee 



