The word 'jasper' is derived from
the Semitic languages; and from the confused description of Theophrastus
('De Lapidibus', 23 and 27) and Pliny (xxxvii., 8 and 9), who rank jasper
among the "opaque gems," the name appears to have been given to fragments of
'jaspachat', and to a substance which the ancients termed 'jasponyx', which
we now know as 'opal-jasper'. Pliny considers a piece of jasper eleven
inches in length so rare as to require his mentioning that he had actually
seen such a specimen: "Magnitudinem jaspidis undecim unciarum vidimus,
formatamque inde effigem Neronis thoracatam." According to Theophrastus,
the stone which he calls emerald, and from which large obelists were cut,
must have been an imperfect jasper.
This opinion is corroborated by the accurate observations on the phenomena
of contact, by the remarkable experiments on fusion
p 262
made by Sir James Hall more than half a century ago, and by the attentive
study of granitic veins, which has contributed so largely to the
establishment of modern geognosy. Sometimes the erupted rock has not
transformed the compact into granular limestone to any great depth from the
point of contact. Thus, for instance, we meet with a slight transformation
-- a penumbra -- as at Belfast, in Ireland, where the basaltic veins
traverse the chalk, and, as in the compact calcareous beds, which have been
partially inflected by the contact of syenitic granite, at the Bridge of
Boscampo and the Cascade of Conzocoli, in the Tyrol (rendered celebrated by
the mention made of it by Count Mazari Peucati).
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