498 ECONOMICAL QUESTIONS. CHAP. 



stone from Yorkshire, slate from Wales, road-stone from Nuneaton, 

 and paving-stones from Charnwood Forest, in addition to the 

 large supply of quartzose pebbles which are gathered from the 

 surface and found useful in jthe streets. The use of all these 

 varieties of stone is quite modern, the effect of railways and canals. 

 Stonesfield still supplies a little of oolitic flagstone rather than slate ; 

 the roads are still mended to a considerable extent by some of 

 the native rocks ; and better stone, for durability at least, than 

 that of Bath, is still quarried in the neighbourhood of Bur ford. 

 Oolite of inferior reputation is common enough in Oxfordshire and 

 Gloucestershire ; and lime is everywhere to be obtained at short 

 distances and moderate cost, though not of any special reputation. 

 The map, Plate II., shews the distribution of gravel near Oxford. 



BRICKS, TILES, POTTERY. 



All the clays in the oolitic series of strata are fit for making 

 bricks, tiles, pipes, and ordinary pottery, if sand be added to the 

 tough argillaceous element, and this is seldom far to seek. In the 

 lower cretaceous rocks thegault, and in the supra-cretaceons deposits 

 the Woolwich clay, London clay, and brickearth of later geological 

 date, supply abundance of material for the kiln. An unusual 

 process is followed in the case of the last mentioned clays at Gray's- 

 Thurrock and other places, where the clays are mostly very sandy. 

 The chalk, which is often dug in the same pit, is ground fine and 

 mixed with the clay, 'to strengthen it.' The heat-action of the 

 kiln not unfrequently appears sufficient to compel the formation 

 of silicate of lime by fusion, and produce clinkers ; but by employ- 

 ing moderate firing this does not happen, and the bricks sometimes 

 appear softer and more sandy than in the districts of oolite, lias, 

 and red marl. 



OCHRE, FULLER'S-EARTH, GLASS-SAND, AND 

 POTTER'S-CLAY. 



< Among such earths as are found in Oxfordshire and are useful 

 in trades/ says Dr. Plot, ' the ochre of Shotover no doubt may 

 challenge a principal place, it being accounted the best of its kind 

 in the world ; of a yellow colour and very weighty ; much used 



