1 823 .] Clay Slate for Road-making. 411 



The material is not favourable to the growth of grass, which is 

 another advantage ; roads of common clay slate and of limestone 

 are often edged'by a grassy bank, which, if it be not frequently 

 removed, confines the water, and so forms a water-course on the 

 road. Garden walks of this material are durable and conve- 

 nient, bein°- but little overrun with weeds, but it must be con- 

 fessed they have a sombre appearance. 



The districts in which this material is employed are in the 

 county of Down, between Downpatrick and Ballynahinch, Bal- 

 lynahinch and Clough Banbridge and Tandaragee, and between 

 Belfast and Bangor; in the county of Armagh, Market Hill and 

 Armagh, and from Armagh to Castle Blayney, in the county of 

 Monaohan. In the south of Ireland, between Waterford and 



The stone from Dunmeniss, near Ballynahinch, being submit- 

 ted to analysis in the usual manner, viz. by fusing it with an 

 alkali, yielded the following constituents : 



Silica 59>4 



Alumina \7'£ 



Lime -' 1 



Magnesia • • • • * * 



Oxide of iron H'° 



Water 6 " 4 



Charcoal and manganese Trace 



Loss 7 0-9 



100-0 

 William Stokes. 



Article IV. 



Observations on Gas Light Establishments, with an Account of 

 some Experiments made to determine the comparative explosive 

 Force of Carburetted Hydrogen Gas and Gunpoxcder. By Sir 

 William Congreve, Bart. FKS. &c * 



The first observation that arises on taking a general view of 

 the gas works in the metropolis, is the immense extent to which 

 they & have now been carried since the year 1814, when there was 

 only one gasometer of 14,000 cubic feet in existence in Peter- 

 street, Westminster, belonging to the chartered company as they 

 were termed ; the only company then established. Whereas 

 at present, there are four great public companies established, 

 having, altogether, 47 gasometers at work, capable ol contain- 



• From Reports on Gas Light Establishments. Ordered to be printed by the House 

 of Commons, March ^G, ls l i3. 



