depth of earth over the line of the top of the tunnel is reached and the problem of getting over or through it iron was the preferred material, taken presumably for increased to at least twenty feet. The depth of water its fire-resisting quality. But conflagrations like at the critical places is… … compressed air system of tunneling, which has been answers perfectly, it is said, but its great cost precludes the sustaining a vertical heading, has been met, to a SECTION OF RE-ENFORCING FILLING OVER THE TOP its use, except, perhaps, for some particular purpose, great extent, by the shield. This,…
Munn · Mining · Diamond · Debris · Patents · Scientific American · Diamond cutting · Bearing blocks · Mining debris · Express money · Hydraulic mining · Electric light · Post office · Sulphurous acid · American supplement
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