195 



dress the contents of the "dead heaps;" in some cases with con- 

 siderable profit to the miner. 



The second group of Anhydrous Carbonates comprises such as 

 crystallize in the Hexagonal System. 



Next to Quartz, Calcite, Calcic Carbonate, is by far the most 

 widely-diffused mineral occurring in the two counties. This is 

 especially the case in the part of the district occupied by the 

 Carboniferous Limestone Series. The mineral occurs in an almost 

 endless variety of crystalline combinations ; and it is hardly too 

 much to say that within the limits of the district under consider- 

 ation, as great a variety of crystalline forms of this mineral are to 

 be found as may be gathered from the mines of all the rest of the 

 world put together. It may be worth while again to direct attention 

 to the fact, already alluded in the case of Aragonite, and long 

 well-known to practical men, that particular crystalline forms, or 

 crystalline combinations, prevail at particular localities, while the 

 same mineral obtained from adjoining localities, perhaps from 

 veins of the same kind traversing rocks of precisely the same 

 nature, and, to all appearance, produced under just the same 

 circumstances, may be characterized by forms entirely different. 

 This is true, of course, of many other minerals than Calcite, and is 

 sufficiently well known to miners and persons accustomed to handle 

 large numbers of minerals from a variety of locaHties as to enable 

 them to decide, in many cases without the slightest hesitation, 

 what particular district, or even what particular mine, a given 

 mineral may have come rom. To describe these differences, in 

 the case of the mineral under notice, would involve crystallographic 

 details a little out of place in a paper like the present ; but it is a 

 subject that has been by no means worked out, and might well 

 form the subject of a series of investigations by some of our local 

 mineralogists, or others that have the requisite variety of specimens 

 before their eyes. As instances of some of the varieties of form, I 

 would refer to the combinations of obtuse- and acute-rhombohedra, 

 and of these with hexagonal prisms, which are common in the 

 Alston district; the large prisms with a combination of the terminal 



