540 A Geogmstical Sketch of [Nov. 



it constitutes the 11th lime-stone bed, reckoning from the surface, 

 and is about four fathoms thick. I am certain at least that it was 

 at no great distance from Alston that I met with this bed. The 

 second exception is a thin bed of limestone (the ninth bed from the 

 surface), not a yard thick, quite full of shells, and known by the 

 name of Cockle-shell Lime-stone. 



But the three best known lime-stone beds are called the Scar 

 Lime-stone, Little Lime-stone, and Great Lime-stone. The Scar 

 Lime-stone constitutes the roof of the level driven in the direction 

 of the river Kent, from the town of Alstone, towards Nent Head. 

 This level has been cut at the expense of Greenwich Hospital, to 

 which that tract of country belongs, and has been working these 30 

 years past. It has now advanced about five miles ; but has still 

 several miles farther to go. 1 went up this level nearly to its head, 

 and learned more respecting the directions, and relative ages of the 

 veins that traverse these beds than I could have done by visiting 

 perhaps all the lead-mines in the district. The Scar Lime-stone 

 constitutes the eighth lime-stone bed, reckoning from the surface. 

 It is a hard blue lime-stone, about five fathoms thick. The word 

 scar in this part of the country is applied to a rock. Hence pro- 

 bably the origin of the term. 



The Little Lime-stone is the 13th bed of lime-stone, reckoning 

 from the suiface ; and is so called to distinguish it from another 

 bed, which lies at some distance below it, constituting the loth bed 

 of lime-stone, and is called the Great Lime-stone, because it is the 

 thickest bed in the formation. The thickness of the Little Lime- 

 stone bed is about three fathoms ; that of the Great, about twelve 

 fathoms. The lime-stone in both is blue, hard, and destitute of 

 petrifactions. These two beds, especially the last, interest the 

 managers of the lead- mines in these districts more than any of the 

 others, for a reason that will soon appear. 



3. The rock called slate clay by mineralogists is distinguished in this 

 district by the name of plate, doubtless because it is composed of 

 plates lying above one another. The beds of slate-clay are very- 

 numerous, amounting, as far as I could make out, to above GO. 

 They are mostly thinner than the beds of the other minerals, those 

 of coal excepted. This thickness seldom exceeds five or six 

 fathoms, and is usually much less. I was told indeed of one very 

 thick bed of slate-clay; but I did not see it. It was not far from 

 the lowest in the series of beds. This slate-clay varies very much 

 in hardness in different beds; sometimes it is so soft as to crumble 

 readily to powder on exposure ; sometimes so hard as to require 

 being blasted by gunpowder. In this last state it is called whin by 

 the miners. When I first heard the term whin-stone in Northum- 

 berland, I naturally applied to it the meaning which it bears in the 

 south of Scotland, and conceived that it signified green-stone, 

 basalt, or porphyry -si ale. But the sight of a few specimens of 

 whin from the miners soon convinced me that 1 was mistaken. The 

 term is not limited to any particular species of rock, but alludes 

 solely to the hardness. It is applied indifferently to sand-stone and 



