OF THE MENAI BASIN. 
235 
kinds, the blue, the red, and the green. The blue^ being 
most preferred, is the most valuable to the proprietor, though 
the other two are equally durable. These veins are includ- 
ed between hard dark-coloured greywacke rocks, and are 
penetrated through, from the north to south, by a sparry 
vein containing pieces of galena, and now and then sul- 
phuret of copper. This dike deranges the structure of the 
slate near it, and renders it unfit for splitting. 
This quarry surpasses all others in convenience of re- 
moval of rubbish. Placed on a high steep face of a hill, 
the refuse is easily got rid of, and all obstruction in the 
working of it is prevented. On a railway of iron, seven 
miles long, extending to the Menai Strait, the slate is con- 
veyed to the shipping. 
In this quarry of Alt Dhu 800 workmen are generally 
employed. 
The situation of these quarry men is often exceedingly 
perilous. In the course of boring and blasting the slate- 
rock, they have to descend by ropes perpendicularly 100 
feet or more ; and, in this position, suspended in the air, 
they fearlessly proceed in their operations. 
How fearful 
And dizzy 'tis to cast one's eyes so low ! 
The crows and choughs that wing the midway air 
Show scarce so gross as beetles : half way down 
Hangs one that gathers samphire ; dreadful trade ! 
Methinks he seems no bigger than his head." 
Shakspeare. 
Two ropes are employed by these men ; the one they coil 
round their body and one of their thighs ; and the other 
rope they hold in their hands, and with wonderful dex- 
terity, raise or lower themselves at pleasure. 
Good workable slate is raised also in considerable quan- 
tities at Clogwyn, on the western bank of the lake of 
Llanberris, nearly opposite to that of Alt Dhu, and on the 
