484 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 30, 



masses. The friction has produced a considerable quantity of frag- 

 mentary pyrites of the size of gravel, which is all washed and em- 

 ployed. I believe I am correct in asserting that iron-pyrites is 

 nowhere found with the serpentine, even along with the ores of 

 copper. One of the greatest advantages in working these mines 

 is the softness of the steatitic rock. Other mines are established at 

 Libbiano, Monte Castelli, &c. : they are newer, and have been hitherto 

 less fortunate. Most probably, as Prof. Pilla observed, the deposits 

 whence the rich outlying indications proceeded will be met with 

 further down. 



Closely associated with the serpentine, chalcedony is found in large 

 quantities north of Monte Verdi; it occurs in regular veins, of consider- 

 able size. The mineral is found in blocks smooth at the surface and 

 mammillated internally — often cavernous. I saw some remarkable 

 masses, several feet long, in which small pieces had been cemented 

 together by a fresh development of chalcedony, resulting in a com- 

 pact siliceous conglomerate without any flaw. The pebbles were 

 principally buff-coloured or green, the cement colourless. The 

 neighbourhood affords specimens showing every gradation between 

 opaque black flint, jasper, agate, chalcedony, and waxy opal. 



Alabaster. — Pure-white alabaster is, I believe, peculiar to "Western 

 Tuscany, where it occurs in the Yal di Marmolajo, twenty-five miles 

 from Volterra, and eighteen from Leghorn. It is found in smooth 

 ovoidal masses, sometimes attaining three feet in diameter. 



The general section is : — 



1. 6 feet light-blue bituminous marl. 



2. 6 ,, greyish marls with selenite. 



3. 6 „ bituminous marls. 



4. 5 to 10 „ marls and clays containing masses of alabaster, 



irregularly disseminated. 



5. 6 to 10 „ marls and clays, and gypsum-beds with bitu- 



minoxis odour. Beds like No. 1. 

 6-10. Alternations of strata like the above ; three of them 

 containing alabaster. 



Pure alabaster is not found in direct contact with tbe surrounding 

 strata, but enclosed in an envelope of ochrey-yellow selenitic marl, at 

 least an inch thick, firmly adhering to the surface ; it is worked by 

 pits, entrance being effected laterally, or by wide shafts. The distance 

 between the lumps is frequently many yards ; four or five rows occur 

 irregularly disseminated. None but the pure white is extracted in the 

 Yal di Marmolajo. In the numerous interstices or fissures between 

 the marly strata, often an inch or two wide, are found splendid 

 limpid crystals of selenite attaining nine inches in length. 



Pure alabaster is confined to the Miocene in Tuscany ; but the 

 coloured varieties extend into the Pliocene beds, and are even being 

 produced at the present day. The heat to which the alabaster-beds 

 have been subjected was very inferior to that of the soffioni, whence 

 boracic acid emanates, as I have elsewhere pointed out*, and where 



* See Journal of Soc. of Arts, May 23, 18G0, and several successive papers in 

 the same periodical. 



