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plane and one or more sets of rhombic faces, from Greenside ; the 

 thin, disc-like, tabular crystals occurring at both the last-named 

 localities ; the aggregations of small prisms with rhombic ends 

 built up into groups having the external form of large scalenohedra, 

 which are found in such perfection at Helton ; and many others 

 whose mere enumeration would alone be sufficient to occupy four 

 or five of the present pages. 



Calcite occurs of various shades of colour, from perfectly clear 

 glassy crystals through various shades of cream colour, grey, or 

 pale brown, to salmon colour, or rose. Encrustations of radiating 

 crystals of the last-named tint occur in connection with the Car- 

 boniferous Limestone near Kendal. 



Other forms of Calcite, or what is commonly regarded as such, 

 are the stalactites and stalagmites found in caverns in limestone 

 districts, as well as the travertine from calcareous springs. Mr. 

 Bryce M. Wright, in his List, refers to good examples of this last 

 at Park Head, near Hesket-New-Market. Others of the same 

 kind are of general occurrence wherever springs are thrown out at 

 the junction of any widely-jointed limestone rock and an imper- 

 vious bed beneath it. 



Calcite very commonly appears as a pseudomorph retaining the 

 external form of some other mineral, which has been gradually 

 removed in solution, while Calcite has as gradually occupied the 

 vacant space. Very frequently crystals of one kind have been 

 invested with a coating of minerals of a kind quite different ; then 

 the first-formed mineral has been removed in solution, and the 

 vacant space it occupied either filled with other substances or else 

 left vacant. As a rule it is the more stable compound that stands 

 longest, and the least stable that is first to go. But Professor H. 

 A. Nicholson called my attention some years ago to a remarkable 

 exception to this rule, occurring at Dufton. In this, crystals of 

 Barytes, one of the most insoluble substances known, had been 

 invested by Calcite, and afterwards entirely removed in solution, 

 leaving the cavity it formerly occupied entirely empty. What the 

 solvent was that brought about the removal of the Barytes without 

 affecting the easily-acted-upon Calcite, is not by any means clear. 



