A Treatise on Slate and Slate Quarrying: Scientific, Practical, and Commercial

amount Arenig Average weight Bala bands blocks blue slates Cambrian Carnarvonshire CHAMBERED QUARRY Cilgwyn colour Corris district Corwen cost crychs deposit described Devonian Dinorwig ditto dresser Duffwys failures feet Festiniog district gallery Geological Grit Band grits hard rock hill-side inches incline iron lease Limestone Lingula flags list price Llanberis Llandeilo group Llangollen Llangollen district Llangynog LOWER CAMBRIAN STRATA machine house mass material Merionethshire mineral Minllyn Nantlle North Wales Old Vein open quarry ordinary particulars Penrhyn Penrhyn Quarries porphyritic porphyritic rock portion Portmadoc poundage produce Purple Slates pyrites rails railway Rhiwbach Rhiwbryfdir Roofing slates royalty shaft Shales side SLATE AND SLATE Slate Bargain slate beds slate range slate rock slate waggons slaty cleavage sparry veins split splitter strata thickness thin thousand of 1,200 tion Tons Cwts tramway tunnel underground quarry UNIVERSITY CALIFORNIA CHAPTER upper usually Welsh slates Wenlock