10 Scientific Proceedings, Royal Dublin Society. 



naturally-rounded ones procured from the drift, or the beaches of 

 rivers, lakes, and the sea, or some other natural accumulations. 

 Sometimes they were well selected, both as to hardness and size ; 

 but often this was not so, as is at present the case in parts of the 

 city of Glasgow and elsewhere ; and consequently the surface after 

 a time became rough and uneven. This appears to be one of the 

 great reasons why, at the beginning of this century, Macadam's 

 plan of making roads with broken stone was received with such 

 great favour. 



The early artificial paving- stones, or setts, seem to have been 

 principally made of soft materials, that split readily ; and in this 

 country they were generally of limestone, or other soft materials, 

 that are now universally condemned. The setts in the market 

 seem to be generally classed by the trade as black setts and white 

 setts. The first formerly included both the limestone and the 

 whinstone, although the term is now more generally appropriated 

 to the latter ; while " white setts " include the granite and the 

 grits. Limestones are classed by themselves. 



The stone for paving-setts should split easily, thus requiring 

 little or no after-dressing. It should be durable, that is, capable 

 of resisting crushing and surface wear; and when subjected to 

 traffic its surface should not become soapy or glassy. It is, how- 

 ever, very difficult to find a stone having all these qualities 

 combined. Many of the limestones split easily, and are cheaply 

 wrought ; but in general they are friable or soft ; while those 

 that are tough or silicious, especially the first, receive a more or 

 less soapy polish. Limestone- setts are suitable only for places 

 where there is very little traffic ; but on account of their cheap- 

 ness they can very profitably be used for pathways. The whinstones 

 almost always are hard, durable, and capable of resisting crushing 

 and wear ; but they have to be selected with great care, as many, 

 especially some of those that are tough and hard, readily acquire 

 a soapy-polished surface, which makes them unsuitable for a good 

 pavement. Granites perhaps make the most comfortable road ; 

 but they are generally less durable than whinstones ; while the 

 hardest or quartzose varieties are liable to take a glassy polish. 

 Grits are very variable in character, from open to compact and 

 quartzose. Some of the hard quartzose grits split, or rather break 

 up naturally into sizes suitable for setts, and consequently can be 



