Position In Quarry

In order to obtain the best stone that a quarry can furnish, it is often important that it should be taken from a particular stratum.

Fig. 1.

It frequently occurs that in the same quarry some beds are good, some inferior, and others almost utterly worthless for building purposes, though they may all be very similar in appearance.

To take Portland stone as an example. In the Portland quarries there are four distinct layers of building stone.

Fig. 1 is a section showing approximately how the strata in a Portland quarry generally occur.

Working downwards, the first bed of useful stone that is reached is the True or Whitbed Roach - a conglomerate of fossils which withstands the weather capitally. Attached to the Roach, and immediately below it, is a thick layer of Whitbed - a fine even-grained stone, one of the best and most durable building stones in the country; then, passing a layer of rubbish, the Bastard-Roach, Kerf, or Curf is reached, and attached to it is a substantial layer of Basebed.

The Bastard-Roach or Basebed-Roach and the Basebed are stones very similar in appearance to the True Roach and Whitbed; but they do not weather well, and are therefore not fitted for outdoor work.

Though these strata are so different in characteristics, the good stone can hardly be distinguished from the other even by the most practised eye.

Similar peculiarities exist in other quarries.

It is therefore most important to specify that stone from any particular quarry should be from the best beds, and then to have it selected for the work in the quarry by some experienced and trustworthy man.

The want of this precaution led to the use of inferior stone (though from very carefully chosen and good quarries) in the Houses of Parliament.