274 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



1st. The first line, commencing between Pistoja and Prato, 

 passes through Castello and Fiesoli, and keeping to the N.E. of 

 Florence, descends in a S. E. direction to Arezzo. Castiglion 

 Fiorentino, Cortona, &c, when it passes to the N.E. of the Lake of 

 Thrasymene. 



2d. Commencing to the S. of Pistoja in the Monte Albano, the 

 second line crosses the Arno, between Signe and Empoli, and 

 passing through Galluzzo and L'Impruneta, extends through San 

 Martino, San Donato, Incisa, Levane, to the hills of Chianti, and 

 thence to Monte Cetona. 



3d. The third line, more to the S.W., may be said to commence 

 with the hills of Monte Pisani, near Pisa ; thence crossing the 

 Arno, it continues along the line of hills which separates the valleys 

 of the Era and the Elsa, passing between Volterra and Poggibonzi 

 until it reaches the mountainous district, in which are the quarries 

 of Sienna marble, ten or fifteen miles S.W. of that city. 



Perhaps a 4th parallel line may be traced further to the S.W., 

 commencing with the hills of Monte Rotondo, near Leghorn, and 

 passing through Monte Catini and Monte Cerboli, until it loses 

 itself in the complicated system of the Maremme.* 



It is still a question for further investigation how far the 

 crystalline limestone near Sienna, and in which, to the W. and 

 S. W. of that town, are the quarries of Sienna marble, is to be con- 

 sidered as a district of older formation. It is probable that a 

 transverse chain of elevation, marked by rocks of a more crystalline 

 character, will hereafter be distinguished extending from N.E. to 

 S.W., i. e. from the Monte di Chianti, through Monte Maggio, N. of 

 Sienna, to the district in which the quarries occur. 



The valleys between these different ranges are generally filled with 

 tertiary deposits of various characters, some of a mere local nature, 

 while others extend over a considerable tract of country, to which 

 they impart a singularly dreary appearance, being almost entirely 

 devoid of vegetation and altogether unsuited for cultivation. 



The various formations of Tuscany may be described in the fol- 

 lowing ascending order : — 



A. Stratified Rocks. 

 I. Secondary formation. 



C 1. Tertiary marine. 

 II. Tertiary formation -2 2. Tertiary freshwater. 



(_ 3. Post-tertiary formations. 



B. Metamorphic Rocks 



Red Gabbro. 



C. Igneous Eocks. 



1 . Serpentine — secondary period. 



2. Selagite — tertiary period. 



3. Basalt of Radicofani, &c. 



* Since writing the above, I find that the same features of three parallel 

 ranges have been described by M. A. Burat, in a paper lately read before the 

 Tnstitut de France. See Comptes Bendus, 1843 (p. 1279.). 



