590 



CHAPTER XXXV. 



INDUSTRIAL PRODUCTS OF THE GEOLOGICAL FORMATIONS 



ORIGIN OF LODES QUANTITIES OF AVAILABLE COAL 



IN THE COALFIELDS ORIGIN OF THEIR BASIN-SHAPED 



FORMS CONCEALED COAL-FIELDS BENEATH PERMIAN, 

 NEW RED, AND OTHER STRATA SUMMARY. 



To enter into detail upon the peculiar effect of geology 

 on the industry of the various races or the populations of 

 different districts, would lead me far beyond the proposed 

 scope of this work. I shall, therefore, only give a mere 

 outline rather than attempt to exhaust the subject. 



First, let us turn to the older rocks. In Wales, as I 

 have already stated, these consist to a great extent of 

 slaty material. The largest slate quarries in the world 

 lie in the Cambrian rocks of Caernarvonshire. One 

 single quarry, that of Penrhyn in Nant Ffrancon, is 

 half a mile in length, and more than a quarter of a 

 mile from side to side. Other quarries of equal impor- 

 tance collectively occur in the Pass of Llanberis, and 

 there are large quarries in the same strata at Nant-y- 

 llef, but none of these are of the same vast size. Im- 

 portant quarries also lie in the Lower Silurian rocks 

 near Ffestiniog in Merionethshire, and there are large 

 slate quarries in the Wenlock shale, near Llangollen, 

 and others of minor note scattered about Wales, but 

 always in Cambrian or Silurian rocks. 



