Hull — On the Different Varieties of Irish Paving-Setts. 97 



iron gives to these rocks a higher specific gravity than those of the 

 granitoid class, in which iron is either absent or occurs in exceed- 

 ingly small proportions. Thus, while the average specific gravity 

 of granitoid rocks may be taken at 2*65, that of the whinstones 

 may be taken at 3'0 ; so that, in the case of a contract for 

 purchase by weight, the granitoid rocks are in favour of the 

 purchaser. 



The rocks of the " whinstone " class are generally exceedingly 

 tough, and setts taken from them are capable of withstanding the 

 heaviest traffic ; but their chief defect is the tendency to wear into 

 smooth surfaces and become slippery. Being essentially compact 

 in structure, the component minerals are incapable of individually 

 disintegrating, and thus preserving a rough exterior where subjected 

 to wear and tear. This is the case, at least, with regard to the 

 finer and denser varieties ; and it is therefore important, in select- 

 ing a stone of this class for paving purposes, to see that it is 

 largely crystalline-granular, as such varieties will be less liable to 

 wear smooth. 



Quarries for making paving-setts from whinstone have been 

 for some time past opened at Ballintoy, Co. Antrim, and Arklow, 

 Co. Wicklow. The Welsh setts from the quarries at Penmaen 

 Mawr belong to this group, and have been largely used not only 

 in England but in Ireland, where stone of similar or identical 

 qualities is to be found in abundance. The great obstacle to the 

 manufacture of paving-stones in this country has been — not so 

 much want of capital or enterprise on the part of the employers of 

 labour — as want of knowledge in the art of shaping the stones on 

 the part of workmen. This want is now being supplied, as Irish 

 stonemasons are being instructed by workmen from Wales and 

 England ; and as we possess abundance of the raw material, we 

 may look forward with hope to a large and flourishing trade in 

 various parts of the country. 



In considering the qualities of different varieties of paving- 

 setts, and the purposes to which they should be applied, I think 

 we may fairly come to the conclusion : — that for streets subject to 

 excessively heavy traffic, the whinstone varieties, especially those 

 of largely -crystalline structure, are the more suitable; while for 

 streets with ordinary traffic, those of the granitoid class will be 

 found sufficiently durable, and, from wearing rough, more advan- 

 tageous. 



