HAMILTON ON THE GEOLOGY OF TUSCANY. 281 



and green and yellow veins. It is frequently much shattered, and 

 sometimes mixed up with the blue clay : it is harder than the 

 other varieties, and is used principally in the manufacture of vases, 

 candelabra, &c It occurs chiefly from four to six miles S. E. and 

 E. of Volterra, on the road to Florence. 



2. In the immediate vicinity of the little village of Picchiaiola, 

 five miles on the road from Yolterra to Florence, is a very consi- 

 derable mass of gypsum of peculiar character, rising above the 

 surface of the ground. It consists of irregularly compacted masses 

 of crystals of selenite easily detached from one another, and called 

 by the people of the country specchio (fasino, or the " ass's look- 

 ing-glass." On breaking off the outer crystallised crust, an earthy 

 crystalline substance is perceived full of cavities and botryoidal 

 concretions, precisely resembling the substance formed round the 

 vents of the vapours of Monte Cerboli ; at once suggesting the 

 idea that some at least of these gypseous deposits may have been 

 produced by similar vapours or soffioni. 



3. The third form in which the gypsum occurs in this district 

 is that of an irregular broken stratification. The blocks occur at 

 intervals more or less distant, extending in long lines through the 

 marls in which it is found, sometimes occurring as detached 

 masses, and at others in continuous beds. In the neighbourhood 

 of S. Lorenzo, near the suspension bridge over the Cecina, this 

 formation is seen on both sides of the river, but is not of any great 

 thickness. Near Buviano, on the north bank of the Cecina, to- 

 wards Monte Catini, the gypsum beds occur sloping at a very 

 considerable angle down the hill sides, and apparently following 

 their inclination. Wherever this variety of gypsum occurs it is 

 almost invariably of an opaque white saccharine character. It 

 is found in many detached spots in the Volterra district. 



4. By far the most interesting and important of the different 

 varieties of gypsum is the fine white alabaster found in the neigh- 

 bourhood of Castellina, where it is regularly stratified, and is 

 worked in properly constructed mining galleries. The little town 

 of Castellina, distant about twenty or twenty-four miles from Vol- 

 terra, is reached by a rocky road over wild and rugged mountains. 

 It is situated on the TV. N. TV", slope of the hills of Monte Taso, 

 overlooking in that direction an extensive and slightly undulating 

 plain of tertiary marls, which there can be no doubt extend round 

 the north point of the Monte Vaso chain, and are connected with 

 those of the Val d' Era and the Volterra district. 



The mines are situated three miles TV". X. W. from Castellina, 

 near the edge of the tertiary marls, where they rest against the 

 secondary rocks. They occur on a slightly rising ground between 

 two streams, the Pescera on the south, which flows between it and 

 the hills, against which the blue marls probably once rested before 

 the river bed was washed out, and the Marmolaio on the north, 

 which flows through the marl itself. (See Section, No. 2.) 



