HAMILTON ON THE GEOLOGY OP TUSCANY. 275 



A. Stratified Rocks. 



I. Secondary Formation. 



These rocks, which constitute by far the greatest portion of the 

 mountainous districts of Tuscany, forming the parallel ranges 

 extending from N.W. to S. E., consist of various beds of sandstone, 

 indurated marls and shales, and compact grey lithographic lime- 

 stone or scaglia, either alternating with each other or more or less 

 developed in different localities. 



The sandstone consists of three different varieties, viz., — 



(a) Hard grit (?nacigno), considerably developed near Florence, 

 particularly to the W. and S. W., where it forms large mountain 

 masses, and is extensively quarried along the banks of the Arno, 

 and at various other points, for building-stone and for the slabs em- 

 ployed in paving the streets of Florence. A very considerable 

 quarry, affording an excellent section of thin beds of this rock, 

 alternating with a soft bluish shale, occurs on the banks of the Ema, 

 near Ponte d'Ema, about two or three miles S. E. from Florence. 

 Many of the slabs show slight appearances of fucoidal stems. It 

 generally occurs alternating with thin bands of shale of a dark 

 blue or reddish colour. It varies considerably in dip, although 

 most frequently inclined to the N., N. E., and N. W. The grain 

 of this stone is generally coarse and compact, and it is often tra- 

 versed by thin veins of calcareous spar. 



(b) A fine-grained greenish sandstone (pietra serena), exten- 

 sively quarried near Fiesoli, where the beds dip to the N. W., and 

 used for architectural purposes in Florence. It also occurs at 

 Monte Catini, ^ust above the village of that name, dipping S. 

 and S. E. 



(c) A soft friable sandstone, of a yellowish brown colour, slightly 

 micaceous. It is broken by numerous fissures into rhomboidal 

 masses of various sizes and shapes. It forms hills of considerable 

 height and extent in the Yal d'Arno di sopra, above Levane and 

 Arezzo. I only met with one locality producing anything re- 

 sembling organic remains, and these consisted of a few vegetable 

 impressions. 



The indurated marls and shales are generally associated with 

 the hard grits and sandstones ; but the former are sometimes de- 

 veloped to a great thickness, forming masses of considerable extent, 

 and consisting of numerous strata. This formation came under 

 my notice in the vicinity of Castiglion Fiorentino, between Arezzo 

 and Cortona, and in the neighbourhood of the mines of Monte 

 Catini. In the former locality it is traversed by several thick 

 veins of calcareous spar ; and in the latter it consists of a great 

 variety of thin strata, dipping from the region of the copper mines 

 to the S. and S. W., and underlying a thick formation of secondary 

 lithographic limestone. Numerous beds of indurated shales also 



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