PRECIOUS STONES. 169
In
some cases the stalactites are free, in others they have at a later
stage in growth been surrounded by Chalcedony, and in this case surface
tension has caused the bands to be thicker in the proximity of the
stalactite. Eyed Agates, by the increased surface afforded by minute
tufts of other minerals (often zeolitic), have had an increased growth
of Chalcedony at certain points until the layers have formed small
spheroidal outgrowths, and these spheroids on sections give the
appearance of an eye. Fortification Agates are those which through
numerous " eyes" have had their bands formed with sharp salient and
re-entrant angles. Moss Agates owe their character to an early bursting
in of the Saponite layer in moss-like fragments. Mocha Stones show
dendrites of Pyrolusite along the cracks caused by weathering. Jasper
Agates have Haematite or Limonite in a finely divided state enclosed in
them, causing opacity with a red or yellow colour. Carnelian Agates
have Hfematite enclosures in disseminated spherules. Red Banded Agates
are ordinary Agates in which the absorbent bands have been coloured red
by a subsequent natural staining by Haematite. Bleached Agates are any
of those containing oxide of iron or zeolitic matter which by
subÂsequent change is partly decolorised or removed. The Cloud Agates
are those in which the removal of the zeolitic matter has been
irregular, so as to give a cloud-like effect.
The
distribution of Agates is very wide, but some localities are of
outstanding interest. Thus for long the chief supply of cut Agate came
from Prussia, being not only found there but cut there also. Thus at
Birkenfeld in Oldenberg, Galgenberg near Idar, and Struth near
Oberstein, the material was found in large quantities in the amygdaloid
