80 On the Constitution of the Territory of Rorae, with 



alpine limestone ranges, where the long agitation of the water, and its exten- 

 sive contact with the atmosphere, have furnished the conditions necessary for 

 its formation. Even now similar formations are going on in the conduits 

 which supply all parts of ancient as well as modern Rome with water ; and 

 where the Anio leaves the Apjjenines, by the splendid cascades at Tivoli, we 

 have a similar formation, in a gi-eat scale, under our very eyes. 



The principal masses of this curious limestone lie in horizontal beds and 

 strata. It is yellowish white, of uneven fracture, and earthy grain. On ex- 

 posure to the air, it gains considerable hardness, and usually assumes that 

 reddish hue which gives so peculiar a character to the monuments formed of 

 it, and contributes, in no small degree, to cause that imposing impression of 

 pomp and majesty which they never fail to excite. Leopold von Buch ex- 

 pressly observes, that what is especially characteristic and remarkable in it, 

 are the numerous perforations and vesicular cavities, from which it is never 

 free. These are of two descriptions of cavities, either elongated and narrow, 

 internally dull, and in which vegetable remains often occur, which shew that 

 they are deriv«l from portions of jjlants, which have since disappeared ; or 

 they are large shapeless openings, which seem to have been irregularly com- 

 pressed in a longitudinal direction. Their interior is usually covered with 

 calcareous spar, which has the stalactitic and reniforni external shape ; and at 

 times, when the cavities have again been filled, appear as regular white spots. 

 These openings have most probably arisen from the escape of gases which 

 existed during the consolidation of tlie stone, as is at present the case in the 

 small Lagune of Solfatara near Tivoli, which has been so often described. 



The travertine is ricli in organic remains, but never contains marine j)ro- 

 ductions. They are usually vegetable, particularly in the line extending from 

 the Porta del Poj)olo to Ponte Molle, where many impressions of leaves ot 

 trees, traces of branches and seeds, round which the lime seems to have ag- 

 gregated in concentric layers are found. Every where we see in it the same 

 fresh-water Conchylice above noticed as occurring in the sand and clay of this 

 formation. In the district of Torre di Quinto, opposite Prima Porta, Brocclii 

 found it abundantly associated with the femora of animals resembling frogs. 



The existence and geognostic relations of the travertino is seen often and 

 clearly exposed within tlie hills of Rome, and i)articularly on those at the left 

 bank of the Tiber. The most considerable of these deposites is seen on the 

 declivity of the Aventine, towards the Tiber. It there forms a horizontal 

 bed, at a height of ninety feet above the level of the river, the longitudinal 

 direction of which can be followed in an uninterrupted line for the distance 

 of half a mile. In a pit, which is found within Trelles of No. 14. in the Mar- 

 morata, it is distinctly seen above the river-sand ; which, on that side again, 

 covers the volcanic tufa of this hill. It now and then alternates with strata 

 of calcareous sand, and includes small pieces of pumice-stone, and likewise 

 the usual remains of vegetables and shells of Helix decollata and muralis, which 

 are frequently found alive in the gardens of this spot. Over it lies a stratum 

 of that argillaceous clay which we have already seen to be the principal cover 

 of the plain. 



Single masses, and even thin beds of travertino, are numerous in the 

 sandy and marly strata, even in the upper ones of volcanic tufa, on the slope 



