176 M. Brongniart on the position 



serpentine rock, diallage rock, and jasper, a notice to exa- 

 mine the mountains attentively. We mounted towards an 

 elevated platform here forming the crest of the Apennines; 

 the stratification was nearly horizontal, consequently we 

 presumed that as we rose we quitted the inferior and ar- 

 rived at the upper beds. In fact, after passing the col of 

 lo Stale, on the side of Traversa, in a very hilly canton 

 named, we were informed, Sasso di Castro, the succession 

 of the following rocks begins to shew itself, continuing nearly 

 from Maschere to beyond Covigliano, a short distance tO 

 the south of Pietramala. This succession of rocks becomes 

 even more distinct the nearer Pietramala is approached, 

 and appears well defined in the almost perpendicular moun.' 

 tains on the west of the road. 



1st. The summit A, fig 4, of these mountains, which is^ 

 precipitous, or with a very steep slope, cut by numerous 

 furrows or deep ravines, and bristled by small peaks, or 

 very pointed paps, is composed of hornblende serpentine 

 (ophiolite araphiboleux), and especially of hornblende di- 

 allage rock (euphotide amphiboleuse), resembling green- 

 stone, but which is too soft to belong to that class of rocks. 

 These rocks pass, at the base of the mountain, into serpen- 

 tine diallage rock (B), which here presents a very remark- 

 able variety, which is that it possesses the amygdaloid 

 structure, and all the characters of rocks named amygda- 

 loids (variolite). The white spots appear to me to be pe- 

 trosilex ; they melt very easily before the blow-pipe, but 

 with a very remarkable ebullition. I make a peculiar variety 

 of it, by the name of amygdaloid diallage rock (euphotide 

 variolitique). 



This rock varies in mineralogical structure, and I might 

 long descant on its varieties, if the details had been of use 

 to my subject. It is more or less thick, and enormous 

 fallen masses occur at its foot.* 



• Circumstances not allowing me to remain at Pietramala, I was un- 

 able to climb to the summit of this mountain in order to examine in place 

 the varieties of the serpentine rock composing it : I studied them among 

 the immense fallen masses which cover the sides, and which present 



