86 



to the Rubble Stone of Kirw, v. 1. 366. Sandstones are 

 found in many parts of England, and are of great use. They 

 are natural filters in the laboratory of nature, and are now 

 become a modern branch of traffic in Derbyshire, London, 

 and other places, for filtering water. They are brought 

 from Newcastle for grindstones, sharpening of scythes, 

 rubbing down copperplates, &c. Some sorts have been 

 used for buildings, as at Windsor Castle, which is chiefly 

 of the whiter kind and finegrained. The grey and black 

 blotches will be explained hereafter. Mr. Martyn above 

 mentioned has given figures of several specimens of these in 

 his Derbyshire Petrifactions * 



