458 [Nov. G, 



occur in the neighbourhood of Florence, in the hills above the 

 Certosa, where it is overlaid by thick beds of macigno.* 



The limestone called in the country alberese, and often associated 

 with the above-described sandstones and indurated argillaceous 

 shales, is very compact, varying in colour from a bluish to a yel- 

 lowish white, and resembles lithographic limestone and the scaglia 

 of the N. of Italy and Greece, which is generally referred to the 

 Cretaceous period. The principal localities at which I had an op- 

 portunity of observing it were : 1, near the Impruneta, six or seven 

 miles S. of Florence, where it is extensively quarried. Not far 

 from hence, at a place called Mugnano nummulites are said to 

 have been found in great abundance in one of the limestone 

 beds ; 2, at San Donato, 9 miles S. E. of Florence, on the road to 

 Arezzo, where it forms hills of considerable height. It is either 

 horizontally stratified or dips slightly to the E. It may be traced 

 for several miles to the S, in the bottom of all the ravines, overlaid 

 by tertiaiy sands and gravels, as far as Incisa, on the banks of the 

 Arno ; 3, at Monte Catini ; the alberese here overlies the sandstone 

 and indurated marls which have been upheaved and tilted by the 

 protrusion of the igneous rocks with which the copper mines of La 

 Cava are connected. It laps round the uplifted masses of Monte 

 Massi and Poggio alia Croce, and not possessing the same elas- 

 ticity as the schistose beds, has been much more shattered and 

 broken up by the elevatory action to which it was exposed. It 

 also occurs in the same chain of hills further westward, towards 

 Monte Miemo, where, not being in such immediate contact with 

 igneous rocks, it still preserves its compact and stratified character. 

 Proceeding westward, towards Castellina, it is found in several 

 places near Monte Vaso, where attempts are now making to obtain 

 copper on the strength of indications similar to those of Monte 

 Catini. 



To the S. of the Cecina, in the midst of a wild and wooded 

 mountain district, consisting chiefly of serpentine or ophiolitic 

 rocks, the same scaglia limestone also occurs, forming elevated 

 plateaux and ridges, on which, notwithstanding the enormous 

 fragments by which the ground is encumbered, the industry of 

 the inhabitants is constantly directed to the raising of crops of 

 corn. My attention not having been so particularly directed to 

 these secondary formations, I regret that I cannot more clearly 

 describe the different groups into which they ai'e subdivided. 



II. Tertiary Formation. 



The tertiary formations of Tuscany may, for the purposes cf 

 arrangement, be subdivided into three groups, as already men- 

 tioned : — 



♦ Captain Porlloek's paper has been communicated since this was written. 



