TAB. XXI, Upper Figure. 



CALX sulphurata; var. plumosa. 

 Sulphate of Lime; var. plumose. 



Classrl. Earth. Ord. 1. Homogeneous. 

 Gen. X. Lime. Spec. 5. Sulphate of lime. 



Div. 1. Imitative; var. plumose. 



Syn. Sulphate of lime forming snow-white incrusta- 

 tion, &c. Bab. 29. ccxvi, a, 1. 

 Chaux sulfatee niveforme*. Haiiy, 2. 279. • 



The upper figure is a curious variety of sulphate of lime, 

 or gypsum, from Matlock. It should seem that sulphur of 

 iron or pyrites, by exposure to damp, decomposes ; the sul- 

 phur combining with oxygen forms sulphuric acid, which 

 comes in contact with the lime in the rock, and so forming 

 gypsum, oozes out in these fanciful forms j or, in other 

 words, readily produces gypsum more or less crystallized. It 

 is continually forming in many parts of England. Lord 

 Altamont obligingly sent me some nodules of pyrites,, in 



* A rariery found at Montmartre. 



