1850.] MURCHTSON EARLIER VOLCANIC ROCKS OF ITALY. 283 



Radicofani are represented under the same colours as Etna and 

 Vesuvius. 



Tracts north of Rome. — No geologist can travel from Radicofani to 

 Rome, nor examine the Campagna di Roma, properly so called, in any 

 direction, without being satisfied that the region is eminently one of 

 volcanic character. He sees around him numerous crateriform cavi- 

 ties, evincing the former action of fire ; but when he more closely 

 examines them, he has little difficulty in perceiving, that although 

 volcanic in a general sense, they are distinct from the craters of 

 Central France, for example, or of any other region in which atmo- 

 spheric or subaerial volcanos have operated. In the Campagna there 

 is no trace of the broken-down side of a crater, and still less of any 

 currents of subaerial lava which flowed from such depressions, like 

 those which so decisively demonstrate the origin of the currents or 

 " cheires " of Auvergne. On the contrary, all the stratified accu- 

 mulations of basaltic rocks, tufa, sand, lapilli, puzzuolana, travertine, 

 or gravel, indicate most clearly that they have all been formed or 

 rolled under water. Among the oldest, and at the same time the 

 most crystalline of these rocks, is the basaltiform felspathic grey- 

 stone with quartz crystals of iolite or prismatic quartz, the tephrine 

 lava of Brongniart, which occupies the rugged hill of Radicofani, 

 about 2470 French feet above the sea, and a few miles only to the 

 east of the higher trachytic mountain of Amiata. 



The chief remark I have to make on this rock is, that it seems to 

 have been thrust up through a basin of tertiary subapennine marls, 

 a portion of which it has overflowed and covered, just as many of 

 our Hebridian trap rocks (to use a British illustration) have been 

 protruded through, and have surmounted, our oolitic shales. The 

 Marquis Pareto also describes the tephrine of Radicofani as overlying 

 the tertiary strata ; but Pilla believes it is so old, that the subapen- 

 nine marls were accumulated around it subsequent to its emission. 

 The utter dislocation however of these marls, where they are visible 

 amid the masses of detritus on the slopes of the hills, convinces 

 me, that the igneous rock burst through them at Radicofani, and 

 then overflowed them. There are some appearances as if currents 

 of lava had proceeded from this mountain of Radicofani, but they 

 are soon broken off, and are traceable only in loose dismembered 

 blocks which spread over the slopes, particularly to the south. On 

 descending from the mountain, and after travelling to the opposite 

 bank of the Paglia, we find what I consider to be the same tephrine 

 lava regularly stratified in the escarpment above Ponte Gregoriano, 

 north of Acquapendente, where the Papal States are bounded by 

 Tuscany. The blue subapennine marls, fig. 1 «, p. 284, are there well 

 exposed at the base of the cliff, partially covered by a thin coating of 

 yellow sand, fig. 1 b, both of them well known in these countries as 

 containing marine shells ; and these are immediately and conformably 

 surmounted by an amygdaloid, the concretions of which are as com- 

 pact and well-filled as any trap -amygdaloid of the Highlands. This 

 is followed by a considerable band of the grey basalt, fig. 1 c, or 

 tephrine lava with leucite, on which Acquapendente, like Radicofani, 



