No. I. — Account of Mount Vesuvius. 207 



the more important individuals, we find several genera of the 

 order Salt among the productions of Vesuvius. We have the 

 volcanic sal ammoniac, and the curious mineral placed in the 

 Appendix of Mohs,* Mascagnine, or sulphate of ammonia, 

 which is formed in mealy efflorescences. Pure marine salt, 

 or muriate of soda, is found in beautiful concretions in the 

 crater. It is probable that sulphate of alumina and vitriol 

 also occur, which are met with in the Solfatara of Pozzuoli. 

 In the genus Limestone, one of the most interesting minerals 

 we have is the compact marble found among the ejected masses 

 of Monte Somma and of Vesuvius. They are brilliantly white, 

 compact, and phosphorescent when placed on burning coals. 

 A great many varieties are mentioned, and none is more re- 

 markable than the blue kind, which is used for imitating the 

 sky in the Mosaic work of Naples. One curious specimen I 

 have of 1822, in which the parts are sometimes so homoge- 

 neous and crystalline as to be semitransparent. How this 

 beautiful limestone should be produced by the volcano out of 

 a country calcareous indeed, but excessively coarse and im- 

 pure, is extremely surprising ; and many have attempted to 

 account for it by the influence of heat under 'pressure, — an opi- 

 nion which, as facts stand, seems very probable. In a speci- 

 men bequeathed by Dr Thompson to the University of Edin- 

 burgh, there said to be coarse limestone, observed actually 

 passing into fine marble. Sir William Hamilton has given a 

 drawing of a piece much more unaccountable, where the 

 marble is actually seen formed round a nucleus or lava. 

 Surely there must have been some misapprehension here. 

 These limestones are among the most interesting productions of 

 Vesuvius, and they contain many of the simple minerals whose 

 names we can do little more than mention. Coralloidal Arra- 

 gonite occurs in lava on Vesuvius in beautiful scopiform con- 

 cretions. My specimen is from the " Torre di Bassano," be- 

 tween Castelamare and Torre del Greco. Under the genus 

 Baryte we have the Witherite 9 which occurs in beautiful silky 

 dendritic concretions in the fissures of the limestone above de- 

 scribed. It is called Barolite at Vesuvius. Under the order 

 Malachite, the genus Acatamite exists in Vesuvius in the 6s- 



* Mohs' Mineralogy, by Haidinger, vol. iii. p. 125. 



