HAMILTON ON THE GEOLOGY OF TUSCANY. 295 



are much, sought after by the statuaries of Florence for orna- 

 mental works ; others contain veins and masses of a fibrous 

 substance, which sometimes closely resembles the fibrous asbestos ; 

 the latter becomes harder by exposure, exactly the reverse of the 

 serpentine itself. Near the south end the serpentine assumes a 

 more scoriaceous character : here the asbestos is more abundant, 

 and in some places penetrates the serpentine with many branch- 

 ing veins ; the people called it " pietra alberisata," from its 

 resemblance to the fibres of a tree fossilized. 



On the south-east side, near the junction of the serpentine with 

 the stratified rocks, altered into red earthy jasper, and either 

 perpendicular, or inclined at an angle of 80°, with a north and 

 south strike, the igneous rock is much decomposed and softened. 

 It is traversed in every direction by numerous veins of carbonate 

 of lime, which, not decomposing so rapidly as the rock itself, stand 

 some inches above the ground, presenting a curious reticulated 

 appearance. 



I did not visit the other spot in the vicinity of Florence in the 

 mountains above Prato, ten miles north-west, where the serpen- 

 tine is also quarried, and is worked up in Florence for ornaments 

 under the name of Verde di Prato. 



2. Selagite of Monte Cat'uii. 



This name of Selagite is given to a quasi-trachitic rock, the 

 only instance I observed of such formations, rising up through 

 the blue marls at the western extremity of the chain of hills on 

 which is situated La Cava and its copper-mines, and on the upper 

 portion of which stands the ancient village, or Borgo of Monte 

 Catini. Its sides present an almost perpendicular face, in which 

 the columnar structure is very visible, but the columns, though of 

 considerable length, are irregular both in size and form. It is of 

 a bluish-grey colour, gritty to the touch, and full of small crys- 

 tallized plates of hornblende or amphibole. It is considerably 

 quarried for building-stones, much used in the neighbourhood. 

 Although apparently unconnected with the serpentine rocks, it is 

 remarkable that this trachitic outburst has taken place almost on 

 the direct axis or line of prolongation of the strike of the ser- 

 pentine masses, which appear to have caused the elevation of 

 Monte Massi and Poggio alia Croce. From the altered appearance 

 of the shelly bed, already described on its north flank, its protrusion 

 probably took place during the early part of the tertiary period. 



3. Basalt of Radlcofani. 



The other igneous rocks to be noticed are the basalts of 

 Radicofani, of which, however, I only introduce the name here, to 

 complete the series, as I had no opportunity of visiting them. 



I cannot conclude this imperfect notice of the geology of Tus- 

 cany without calling attention to the boracic acid works at Monte 



u 4 



