Quarrying and all other branches of surface mining rather than diminishing in importance have become of more and more consequence economically, industrially and particularly with the depletion of high-grade deep-mined mineral reserves. Low-grade minerals require low cost extraction and this in many cases necessitates very expensive mechanized equipment with the cost of individual units running into millions of pounds in the case of large- scale operations with high productivity. There has been, and there still is, a tendency for the smaller single quarries to be amalgamated into groups with...