172 M. BnoNGNiART on the position 



the section resulting fiom it would offer that ruinous aspect 

 that characterizes the prisms named the ruin-shaped marble 

 of Florence. 



This observation ought not to be considered as the des- 

 cription of an isolated fact, nor as the explanation of ruin- 

 formed marbles. It is united to the geological history of 

 these mountains, leading us to determine the geological po- 

 sition of the Florence marble, and reciprocally to establish 

 in a more certain manner that of the calcareous formation 

 which supports the serpentines, diallage rocks, and jaspers. 

 We shall find this ruin-formed limestone in places far dis- 

 tant from this last, and the environs of Florence, in a geo- 

 graphical position, which bears the greatest analogy to that 

 of the formation we are describing. 



The second example, taken like the first from the north- 

 ern side of the Apennines, is the least complete ; we have 

 seen but two different rocks in evident superposition ; the 

 position of the third must be presumed from analogy. 



This second example occurs on the N.W. of Florence, 

 near the small town of Prato, and to the W. of the village 

 of Figline, and on the mountain named Monte-Ferrato. 

 I had the great advantage of being conducted by M. Nesti, 

 and Count Bardi, director of the Florence cabinet, wha 

 has published a very good memoir on the diallage rocks and 

 jaspers on Monte Ferrato. 



This mountain, examined on its southern side, presents a 

 rounded summit, of little elevation, composed of serpentine 

 and diallage, without any distinct stratification, but disposed 

 on the contrary, in irregular masses as it were, separated 

 from each other, yet without really being so, and traversed, 

 by veins of asbestus. It is on the summit of this mass of 

 serpentine that M. Brocchi believes he has found and re- 

 cognised prehnite. 



Beneath this mass, at nearly a third of the moantain's 

 height, and still on the southern side, the jasper appears in 

 the section of a ravine (pi, 1. fig. 3), composed of coarse red 

 jasper, mixed with a little greenish semi-transparent jasper. 

 It is sometimes in thin laminae, sometimes in thick strata, 

 but always so splintery that a solid specimen of the 



