ii., p. 521 and 525. 'Annales de l'Association de la
Propagation de la Foi', 1829, No. 16, p. 369.)
[footnote continues] The relative depth reached at Mount Massi, in Tuscany,
south of Volterra, amounts, according to Matteuci, to only 1253 feet. The
boring at the new salt-works near Minden is probably of about the same
relative depth as the coal-mine at Apendale, near Newcastle-under-Lyme, in
Staffordshire, where men work 725 yards below the surface of the earth.
(Thomas Smith, 'Miner's Guide', 1836, p. 160.) Unfortunately, I do not know
the exact height of its mouth above the level of the sea. The relative
depth of the Monk-wearmouth mine, near Newcastle, is only 1496 feet.
(Phillips, in the 'Philos. Mag.', vol. v., 1834, p. 446.) That of the Liege
coal-mine, 'l'Esperance' at Seraing, is, according to M. Gernaert, Ingenieur
des Mines, 1223 feet in depth. The works of greatest absolute depth that
have ever been formed are for the most part situated in such elevated plains
or valleys that they either do not descend so low as the level of the sea,
or at most reach very little below it. Thus the Eselchacht, at Kuttenberg,
in Bohemia, a mine which can not now be worked, had the enormous absolute
depth of 3778 feet. (Fr. A. Schmidt, 'Berggestze der oter Mon.
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