BUILDING CONSTRUCTION 125 



tiles. Glass Pantiles are obtainable for insertion in pantiled roofs. 

 They can be inserted in an old pantile roof in a few minutes. 



The weight of plain tiles and pantiles for roof covering, along 

 \\ ith their bad weather-resisting qualities, has led to the introduction 

 of a variety of patent tiles with special formations to resist wind 

 and rain. 



Ridges and copes, plain and ornamental, are obtainable in tile, 

 fireclay or terra-cotta for roofs, walls, skews, &c. 



BUILDING STONES. Stones used for building purposes may be 

 divided geologically into two classes, viz., those derived from the 

 igneous rocks and those from the sedimentary rocks. To the 

 former class belong granite, whinstone, trap-stone, &c., and to the 

 latter class sandstone and limestone. 



IGNEOUS ROCKS. Granite varies greatly in composition and 

 colour. Durable granite consists chiefly of about 50 to 60 per cent, 

 of quartz, 30 to 40 per cent, of felspar, and 10 per cent. mica. These 

 proportions vary, but the details may be obtained from any good 

 book on building stones. The colours vary from light to dark 

 grey, light pink to dark red, and, in the case of some Norwegian 

 granites, from light blue to dark green. 



The best granites come from Aberdeenshire, Guernsey, Devon, 

 Cornwall, Westmoreland, and Wicklow in Ireland. By reason of 

 its great strength it is in demand for heavy engineering work, in 

 the piers of viaducts, arches, sea-walls, &c. It is sometimes used 

 for paving setts, but is apt to become slippery. For farm building 

 purposes probably the only use to which granite can be put is that 

 for paving stable-yards in the form of setts. 



Whinstone is a close-grained dark blue or black stone with no 

 definite bed or line of cleavage. It is used principally for road-metal, 

 the aggregate of concrete floors, and for paving setts, being superior 

 in many respects to granite for the latter purpose. In the whin- 

 stone districts it is used for building dry dykes, walls and the walls 

 of buildings, but the building of whinstone in mortar is an art 

 confined to the masons in the whinstone districts. It is not to be 

 recommended for building, as it is inclined to draw damp and sweat 

 on the surface. 



SEDIMENTARY ROCKS. Sandstone consists of quartz in the form 

 of sand, held together by the carbonates of calcium and of magnesia, 

 the oxide of iron and silica, &c. Sandstone is most in demand 

 for rubble building and hewn work, owing to its regularity of 

 texture and workability. The durability of the sandstone depends 

 upon the power of the binding material, and its ability to resist 

 weather. The sand or quartz is, of itself, indestructible. 



