20 
&,4LOON. 
Nat. Mist. 
Jew specimens of the less compound varieties of 
agates, in which common calcedony, carneiian 
and heliotrope respectively form the predominant 
ingredients.—Of flint, a well known mineral 
substance, several interesting varieties are depo¬ 
sited in this case. 
(Case 8.) Contains principally opaline sub¬ 
stances, viz. specimens of tlie noble opal, vvhidi 
owes its beautiful play of colours to a multiplici- 
tv of imperceptible fissures in its interior; the 
Mexican sun or fire opal; the common opal, 
a translucent white variety of which, appearing 
yellow or red wdien held between the eye and the 
light, is called girasol; the semi-opal, agreeing in 
its principal characters with the common : speci¬ 
mens of those varieties which, having the property 
of becoming transparent when immersed in water, 
are called hydrophanes, and vulgarly ocm/ms mundi; 
wood-opal or opalized wood ; jasp-opal, referred 
by some authors to Jasper; the menilite, called 
also liver-opal, found at Menil-Montant, near 
Paris, in a bed of adhesive slate, a specimen of 
which is added. Some varieties of cacholong 
may likewise be referred to tlie opal-tribe.—The 
remainder of this case is occupied by the siliceous 
substance called horn-stone, divided into the con- 
choidal and splintery varieties; the remarkable 
pseudomorphous crj'stals from Schneeberg, in 
Saxony, 
