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NATURE, OCCmiRENCE, AND ORIGIN OF ALUNOGEN. 



and there were very evident signs of recoating in the form of 

 wart-like incrustations, some of which were a half inch in 

 length and rounded. About nine months previous to my 

 visit some sandstone five feet in from the incrustation had 

 been picked out and thrown in a heap at the foot of the cliff 

 and exjiosed to the weather. The lumps of sandstone 

 were coated Avith a spongy coat of the alum material 1^ 

 inches thick in places and the lumps Avere firmly held to- 

 gether by the incrustation. 



It is quite clear from the above that exposure to the 

 weather of the freshly-broken sandstone results in the 

 formation of the incrustation and that the sulphate is 

 present in the sandstone. 



Text-Fig. 31 — View of the incrustation of alunogen on the roof of 

 the cave, showing the concentric arrangement of the layers. 



Scattered through the sandstone there are small rounded 

 nodules of limonite-stained material which resist weathering 

 much better than the normal sandstone. These range in 

 size from quite small pellets up to some Avhich are nearly 

 one inch in diameter. Also throughout the sandstone 

 there are small specks of limonite. 



