352 
[B.N.F.O. 
DESCRIPTION OF PLATE. 
Figure I. — Typical specimen of chalcedony from Carnmoney 
Neck, showing the characteristic reniform or spherical 
crystallisation of the mineral ; the section through the 
spherical concretion to the right shows the central 
crystal of calcite invested by a zone of white zeolitic 
chalcedony. 
Figure II. — Exterior surface of chalcedony from Carnmoney, 
showing the hollow pseudomorphous cavities formerly 
occupied by calcite and zeolites. 
Figure III. — Typical vein of banded chalcedony from Carn- 
money, showing a portion of the rock with the usual 
thin layer of calcite and hullite between the former 
and the latter. This structure is most clearly seen, 
where a small quantity of hullite is almost completely 
surrounded by the chalcedony. The thin white layer 
between the dark hullite and the chalcedony is com- 
posed of calcite. 
AUTHORITIES AND REFERENCES. 
Bischof, Prof. G., 1854. Fehrbuch d. Chem. GeoF — Referred 
to on the growth of quartz from solution. Vol. III., 
p. 636. 
Cole, Prof. G. A. 1895. “Hullite.” — Froc. Belfast Flat. 
Field Club. Series II. Vol. IV., pp. 221-225. 
Gault, W., 1879. ‘On the mode of occurrence and probable 
origin of the Hullite and other siliceous minerals 
found in the volcanic neck of Carnmoney,’ etc. — 
Froc. Belfast Nat. Field Club. Series II. Vol. I., 
PP- 353 - 357 * 
Geikie, Sir A., 1897. ‘The Ancient Volcanoes of Great 
Britain.’ Vol. II,, pp. 272-3. 
