189 



TAB. XC. 



The specimen here represented would, very naturally, be 

 taken for one of quartz, which it much resembles ; and per- 

 haps it might be passed over by casual observation as such. 

 It came from the lead hills near Glasgow, and is very valua- 

 ble. It is figured of the natural size, and has part of a 

 large hexaedral column very distinct, with many eighteen- 

 sided crystals, either like the outline in the middle at the 

 right hand, or like the lower figure at the right hand, with 

 the column interrupted as it were in its formation, giving 

 them the appearance of the buttresses often used in Gothic 

 architecture, and adding many faces to the sides of the 

 crystal, as well as giving additional angles to the faces of 

 the pyramid. They vary much; one is nearly like the left 

 hand hot to?n figure with 13 faces, having a pyramid at one 

 end only. 



T A B. XCL 



This specimen, lately sent me, by favour of Mr. Laing, 

 from Wanlock Head mines, near Glasgow, shows the dis- 

 position of the last mentioned substance to form plated 

 octo-decaedrons and other modifications, inclining to the 

 appearance of sulphate of barytes, by forming a sort of trun- 

 cation on the edges. Thus the left hand figure is truncated 



