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lead mine of Silvera Band, Milburn Fell, and occasionally also- 

 from the mines at Helton, in the same metalliferous area. Another 

 form of Aragonite occurring in thin veins in shale at Dufton, is one 

 of the minerals that have been called Satin Spar. Analyses of 

 specimens of this variety have shewn it to contain as high a per- 

 centage as 4'2S per cent, of Diallogite, or Manganese Carbonate, 

 a mineral that has not yet been proved to exist in a separate 

 condition here. The Satin Spar consists of a succession of en- 

 crusting layers composed of close-set, fibrous, silky-looking crystals, 

 varying, in different layers, from shades of silvery grey to pure 

 glistening' snow-white. Some specimens shew a faint rosy tint. 

 Specimens cut and polished in the direction of the length of the 

 crystals, exhibit the beautiful satiny lustre whence it derives its name. 

 Aragonite from the same district assumes a variety of other forms ; 

 but none that call for any special remark. Forms different again 

 occur in the Alston district, and in the limestone at Harcla Mines, 

 near Kirkby Stephen. 



In the haematite district of West Cumberland, the mines yield 

 very perfect specimens of Aragonite in the form of diverging groups 

 of spire -shaped crystals, some as much as two or three inches in 

 length. Those from Cleator occur in the form of spikes, each 

 individual spike having a contour that rounds with a gentle curvar 

 ture nearly to a point. The transverse section of each separate 

 spike varies in form, probably because the spike itself represents 

 an aggregation of several prisms. The flutings and striations 

 running across the faces of each spike, would seem to indicate, 

 also, that the curved contour is due to what is called an oscillatory 

 combination of planes appertaining to the prism, with others 

 referable to one or other of its observed pyramidal faces. My 

 colleague, Mr. Pringle, has called my attention to a beautiful 

 example of this kind in the case of Quartz, exhibited in the 

 Collection at the Museum of Practical Geology; and has suggested 

 that the above explanation may apply to many cases of crystals 

 with curved contours like the Cleator Aragonites referred to. 

 Crystals of Aragonite similar to these in all essential respects but 

 that of size, occur in the Rowtin Gill- and Brandy Gill Mines ; 



