gallery.] 
NATURAL HISTORY. 
103 
which is Dr. Dee’s show-stone (see Walter Scott’s Demon¬ 
ology), &c. 
Case 21. Common quartz: among the specimens of this 
widely diffused substance, which offers such great variety 
in its external aspect, the more remarkable are the hacked, 
corroded, and cellular quartz from Schemnitz, as also the 
pseudomorphous or supposititious crystals, principally 
derived from modifications of calcareous and fluor spars; 
and, with regard to colour, the blue quartz, called siderite , 
from Salzburg, and the rose or milk quartz, which are both 
used as ornamental stones ;—JLbrous quartzflexible 
sandstone from Brazil;— -fetid quartz, from Nantes; — iron 
flint. In this Case are also deposited several varieties of 
stalagmitic quartz or quartzsinter, the most remarkable 
among which are the siliceous concretions deposited by the 
celebrated hot spring in Iceland, the Geyser; another 
variety of it is the pearl-sinter from Santa-Fiora in Tus¬ 
cany (whence it has obtained the name of florite), and 
from the island of Ischia. With these are placed speci¬ 
mens of the ceraunian sinter or those enigmatical siliceous 
tubes which were discovered in the sands of the Senner 
Heath in the county of Lippe (where, on account of their 
supposed origin, they are called lightning tubes, from 
which name those of fulgurite, ceraunian sinter, astraphya- 
lite, are derived), at Drigg on the coast of Cumberland* 
and latterly, by the late Capt. Clapperton, near Dibbla in 
the Tuarick country, Africa, from which localities speci¬ 
mens are here deposited. The hyalite is placed here as 
a mineral related both to stalagmitic quartz and calcedony. 
— Haytorite, a substance purely sileceous, but presenting 
the form of datholite. 
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- 
