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Commentary |
From A. G. SHORT:
I congratulate the author on his paper and his outline of the methods of investigating old, shallow workings. This is one of the most difficult parts of any investigation, and it is one where laboratory testing and theory cannot be relied upon. The successful evaluation of a site underlain by workings must be dependent on a knowledge of the geology of the area and methods of working, boreholes, excavations, powers of observation and considerable experience in this work.
The author indicated a maximum depth of bell-pits in the order of 40 ft. In his book on Derbyshire, Farey(1811) gives an interesting description of this type of working and quotes 10 yd as a maximum depth. This is almost certainly an understatement, and Pilkington (1789) stated that it was usual not to descend lower than 18 yd.
Electrical-resistivity methods of survey can give a reasonable degree of success under certain site conditions. I have a slide of the iso-resistivity lines produced from a survey where the existence of an adit was proved. Negative results, however, cannot be interpreted as indicating undisturbed ground or the absence of old workings. Reference was made to the site in Doncaster which was underlain by old galleries in the Bunter Sandstone at shallow depth. Access was obtained to the galleries and a full survey carried out.
A. G. Short 26 Abercrombie Street, Chesterfield, Derbyshire, Farey (1811) gives an interesting description of this type of working and quotes 10 yd as a maximum
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