172 
powdery white ahout the gangue has been precipitated, 
covering some, and filling other crystals, so as to appear 
as if filling a case—see the lower right hand part of the 
Jjigure. This white part is granular, almost of the texture 
of Carara marble, but is more perfect in the following spe- 
cimen. 
TAB. CCLXXXVI. 
Tus, and the last figure, have nearly the same form of 
crystallization, and also in some parts the appearance of 
Carara‘tarble more complete, with a very white surface. 
Among the substances concerned in this composition or 
decomposition we find Sulphuret of Iron neatly coating the 
crystals; which are more perfect than those in the former 
figure, few having the corroded or half coated appearance; 
and so accurately-does the Sulpburet of Iron fit upon most 
of them, that it could not have been discerned but that 
they were solid metallic crystals of Sulphuret of Iron, with 
a gold blued steel, or copper-coloured, appearance. These 
so complete-coverings are very thin, and, when magnified, 
are found to be composed of minute bubbles, with-the fine 
mamumillated- appearance of the bubbled fusion belonging to 
metals, although the effect of a fire to produce such a fu- 
sion would certainly have given opacity to the crystals 
covered with it, which the broken ones discover to be 
otherwise; that is, to be Carbonate of Lime. 
I am obliged to my worthy and scientific friend the Rev, 
Dr. Jackson for presenting me with these remarkable spe- 
cimens, from the Dimple mine near Matlock, which give 
a fine idea of the changes passing on, in darkness to us, 
although our excavations, when mining, may let in fresh 
agents to the veins or lodes, which may probably assist in 
them, and may sometimes, though unknowingly, be useful, 
or the contrary. It may, however, be wortha little attention, 
as in some instances it may be of great consequence. 
