XIX. On a Shifted Vein occurring in Limestone.
By the J. Mac Culloch, M.D. F.L.S. President of the Geological Society, Chemist to the Ordnance, Lecturer on Chemistry at the Royal Military Academy, and Geologist to the Trigonometrical Survey.
[Read November 15th, 1812.]
The shifting of veins on a small scale is much more common
than the larger phenomena of this nature, which are nevertheless
of frequent occurrence wherever veins exist. These larger
dislocations are known to arise either from the lateral motion or subsidence
of the containing parts, the sides of the line of fracture
sometimes remaining in contact, and being at others separated by
a vein of another description, too well known among miners to
need any comment here. I know not why mineralogists have sometimes
imagined that such appearances were in the smaller examples
fallacious, and were contemporaneous with the formation of the
containing stone. The vein represented in the accompanying drawings
is at any rate too remarkable to admit of such an explanation,
and its character is sufficiently decided to establish a general rule
in favour of all similar appearances.
The rock in which this shifted vein is contained is a secondary limestone, and was brought from Ireland. The specimen, which formed a mill-stone of six feet in diameter, belongs to the Royal Powder Works at Waltham Abbey.
