78 On the Constitution of the Territory of Rome, with 



the Porta Portese and St Pancrazio, as also on that part of the Janiculus, 

 where the botanic garden is situate ; at the Villa Sante, and in many other 

 places in the vicinity. Leopold von Buch particularly describes similar re- 

 lations at the Vatican, before the Porta Fabbrica, going up to the Osteria 

 Cruciano. We see here sand and fragments several times regularly alter, 

 nating with one another, and united by a calcareous, often obviously sparry 

 cement, full of scales of mica, into a fine grained sandstone, and coarse con- 

 glomerate strata. The sandstone itself is abundantly mixed with little sil- 

 ver-white and black plates of mica, and is consequently very splendent, and 

 its predominant cement gives it an argillaceous aspect ; yet its mass effer- 

 vesces strongly with acids. In the conglomerates, on the contrary, whose 

 calcareous cement is much purer, we can evidently distinguish fragments of 

 red and white quartz, much greyish-white and blackish-grey Appenine lime- 

 stone, blood-red jasper, flint, flinty slate. Similar relations are described 

 by the same observer, on the opposite side of the Janiculus, in the above 

 mentioned hollow between the Porta S. Spirito and Porta Portese. The 

 sandstones and conglomerates are here frequently marked by a greater abun- 

 dance of a siliceous cement, by which they are changed into a pudding-stone, 

 of a peculiar appearance, forming pieces which are easily recognised in the 

 workino- of the sand-pits, by their superior hardness, and which immediately 

 detach themselves. Brocchi informs us also of a solid sandstone bed on the 

 Janiculus, near the wall of S. Pietro, in Montorio ; and on the Monte delle 

 Crete ; on the Janiculus to the west of the wall, where it is found in com- 

 pany with a very fine breccia, with a calcareous cement. Breislak saw the 

 same appearance on the INIonte dei Fornaci, close to the hills of the Vatican. 

 In this superior stratum of our oceanic formation, we seldom meet with 

 organic remains ; yet they belong, it ajjpears, entirely to the great shell de- 

 posite, which covers the summit of Monte Mario, at the Villa Mellini ; and 

 in which, according to Brongniart, the most abundant, as well as the most 

 entire, are large oyster-shells, which bear the nearest resemblance to the Os- 

 trea hippopus. The learned Abbate Gismonde also found here a petrifaction, 

 which had been previously described by Brocchi, in his Conchiliologia foss Suh- 

 appenina. Si Patella of the genus Emarginula. Brocchi mentions, that, on digging 

 the foundation for the saloon of the Museum of Pius Clement, a bone was 

 found which was thought by Brongniart to be the metatarsus of a Palteothe- 

 rium. The remains of the fossil mammalia, which Brongniart appears inclined 

 to refer to this genus, we constantly found in the environs of Rome, and, ac- 

 cording to the express testimony of Brocchi, in the fresh- water deposites. 



Under the sandstone there regularly occurs, when we can observe the struc- 

 ture of the rock, a large mass of bluish-grey clay-marl. Its fracture is fine 

 earthy and large conchoidal ; when moist, it becomes workable, and there- 

 fore is a true Figuline marl. It is found uninterruptedly in the hollow 

 which separates the Janiculus from the Vatican, covering both the bottom 

 of the valley and the declivities of the adjoining hills to a considei-able height. 

 Brocchi describes it as behind the sacristy of St Petei*, on the Vatican, and 

 at the Monte delle Crete, an appendage of the Janiculus. The ancients for- 

 merly used the marl of the Vatican for potter's work, as is shewn by the 

 verse of Juvenal (Sat. V.) : 



" Et Vaticano fragiles de inonte patcllas." 



