gallery.] natural history. 163 
called lightning tubes, from which name those of fulgurite , 
ceraunian sinter , astraphyalite, are derived), at Drigg on 
the coast of Cumberland, and lastly, by the late Capt. 
Clapperton, near Dibbla in the Tuarick country, Africa, 
from which localities specimens are here deposited. The 
hyalite is placed here as a mineral related both to stalag- 
mitic quartz and calcedony.— Haytorite , a substance purely 
sileceous, but presenting the form of datolite. 
Case 22 contains some more of the varieties of common 
quartz : prase, which appears to be an intimate mixture of 
this substance and actinote ;—the avanturino-quartz ; —as 
also some varieties of the cat's eye (mostly from Ceylon), 
in which the chatoyant lustre is generally produced by 
nearly invisible fibres of amianth lodged in the quartzy 
mass.—Part of this Case is occupied by the siliceous sub¬ 
stance called hornstone, divided into the conchoidal and 
splintery varieties; among these are the remarkable pseu- 
domorphous crystals from Schneeberg in Saxony, derived 
from various modifications of calcareous spar; also beauti¬ 
ful specimens of wood converted into hornstone, being the 
wood-stone of Werner; hornstone balls from Haunstadt in 
Bavaria.—Of flint, a well known mineral substance, some 
interesting varieties are deposited. The remainder of 
this and the whole of the following Case are occupied by 
calcedonic substances. Among the specimens of common 
calcedony the most remarkable are, the smalt-blue variety 
from Felsobanya in Transylvania, crystallized in obtuse 
rhomhohedrons; the branched and stalactical calcedony 
from Iceland, &c.; the botryoidal, from Ferroe ; nodules, 
including water (enhydrites), from Monte Berico, near 
Vicenza, where they occur in volcanic rocks. 
Case 23. Calcedonic substances continued: cut and 
polished pieces of calcedony with red and black dendritic 
and other figures, called mocha-stones; varieties with 
white, brown, and black, straight or curved lines, some 
of which were probably among the substances of which 
the costly vasa murrhina of the ancients were made; 
red and yellowish varieties of calcedony called carnelian 
— Plasma .— Heliotrope , an intimate mixture of calce¬ 
dony and green earth, which, when containing disse¬ 
minated particles of red jasper, is commonly termed 
