80 On the Constitution of the Territory of' Rome, with 



Brocchi, in his account of the geology of Rome, distinguishes it into two 

 kinds, differing essentially from one another. 



Is/, Lilhoidal Tufa mSteintuf. Is of a reddish brown colour, with orange spots, 

 owing to pieces of a slaggy pumice-like lava. Its fracture is earthy and almost 

 conchoidal, and is so hard as to be capable of being used as a building stone. 

 It contains white mealy leucites, whose gradual transition into the fresh 

 crystallized substance, has been satisfactorily shewn by Von Buch ; scales of 

 brown mica, crystals of black and green augite, and, more rarely, small por- 

 tions of felspar. Now and then are found round blocks, and angular frag- 

 ments of limestone imbedded in it. A fine grained variety can be distin- 

 guished, which would appear a homogeneous mass, were it not mixed with 

 numerous scales of black and silver white mica. 



It usually appears in the form of large beds, from four to six feet thick, 

 traversed by long, vertical, and oblique fissures, which have probably arisen 

 from the contraction of the mass during tlie process of drying. The fine 

 granular variety, again, has the peculiarity of having a disposition to the slaty 

 structure, on account of the linear arrangement of the scales of mica. 



Of the ancient Roman monuments, the Cloaca maxima is built of it, not 

 of peperino, as is usually stated ; also the part of the under structure of the 

 Tabularium of the Capitol, which is seated on the HUl, whilst its outer co- 

 vering is otpeperino. The same hill contains ancient tufa quarries. In the 

 ruins of the passages in the theatre of Marcellus, we see it cut into blocks 

 shaped like bricks ; in the same way are formed the squares of tufa in the 

 fortress of the Gsetani at the tomb of Ctecilia Metella, and at the corner 

 tower of the new Capitol. 



It appears to be the Lapis quadratus of the ancients, which the Romans, at 

 least in early periods, employed in jiaving the streets. Squares of tufa are 

 ver^' often found forming the foundation of the basalt pavement, as is seen in 

 several parts of the city wall : for example, at the Porta St Lorenzo. Of the 

 two kinds of tojj^t which Vitruvius mentions as occuri-ing in Campania, the 

 Tophus niger seems to be the black stone of Piperinum, which is used in se- 

 veral of the buildings of Pompeii, but the Tophus i~uher is the Roman tufa. 

 The place on the Via Flaminia, on the other side of the tomb of Naso, where 

 the tufa was quarried, and which now bears the name of Pietre Bossa, was 

 called by the ancients Saxa rubra. 



In the dwelling-houses are found squares of a greyish yellow tufl', with 

 pieces of yellow pumice, e. g. in the ancient cellar of the house No. CO, in the 

 Longara, and in the foundations of the Papal garden, on the way from the 

 Lavator del Papa to the Quartero Fontane. Brocchi did not find this kind 

 any where j»i silu. 



The points where this kind of tufa exists within the city walls, are, com- 

 paratively few in number. It forms the chief mass of the Capitoline Hill 

 and is here exposed, both by the precipice of the Tarpeian rock, and by the 



the left hand of the road to Ostia, a mile behind the Tre Fontane. It has 

 exactly the appearance of the lava at Capo di Bove, and contains crystals 

 of Gismondi's Abramle, which is most probably a variety of Harniotome. 

 It is rather a mechanical aggregate of volcanic slags, of lapillo, sand, and 

 ashes, which, carried to a distance from the craters from which they were eject- 

 ed, have been deposited in their present situation. 

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