280 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 13, 



ash-colour, on which Flaminius was defeated by Hannibal, are 

 scarcely to be distinguished from those on which Caractacus made his 

 last stand against the Romans, although the one is either eocene or 

 younger cretaceous and the other Silurian palaeozoic ! I make this 

 remark both as a fair excuse for the older geologists, who in a region 

 so void of fossils had considered this macigno to be an ancient " grey- 

 wacke " ; and still more as a reason why the latter word should never 

 more be used, except in a mineralogical sense. This solid macigno 

 of the Thrasymene and Perugia, graduating upwards into thinner 

 courses with flaglike calcareous bands, is surmounted by the pebbly, 

 sandy, and marly accumulations on which Perugia is built*. 



The whole of the western edge of the Apennines from Foligno to 

 Rome is void of macigno, and the grand trough or basin, between that 

 Apennine escarpment on the east and the ridges of secondary lime- 

 stone of the Siennese and Roman Maremma on the west, is exclu- 

 sively occupied by volcanic and tertiary deposits, through which a 

 few islets or outliers of Apennine limestone, such as Mount Soracte, 

 rear their heads as you approach to Rome. But to the south of 

 Narni and in the Sabine mountains east of Rome, where the lime- 

 stones are manifestly cretaceous, we again meet with overlying num- 

 mulitic rocks and macigno, — not indeed on the external or western 

 face of the chain at Tivoli and Palestrina, but between those places 

 and Subiaco. The chief limestone of this tract, even when in that 

 state of marble called " Occhio di Pavone," has been found to con- 

 tain hippurites. In traversing the chain from Palestrina to Subiaco, 

 I perceived, that whilst it presented a broken and often abrupt 

 escarpment to the plain of the Campagna, the hippurite limestone, when 

 followed across its strike or to the east, soon folds over in rapid undula- 

 tions accompanied by great fractures, and at Olevano is surmounted 

 by an impure sandy limestone charged with nummulites and pectens. 

 The whole calcareous series then plunges under troughs filled with 

 macigno sandstone, precisely similar to that of Tuscany, and which, 

 though weathering externally to rusty yellow and dirty ash-colour, is, 

 when quarried into, the same dull bluish grey psammite with minute 

 grains of black schist, so well known as the building-stone of Florence. 

 These macigno beds are occasionally vertical, and often so broken and 

 squeezed up between the older limestones (with a strike from S.S.E. 

 to N.N.W.), that persons unaccustomed to their relations elsewhere 

 might well be induced to suppose that they underlie the older rocks. 

 At Rojati, however, which stands on a fine thick-bedded macigno with 

 alternating layers of shale, that dips away at a slight angle (this place 

 being near the centre of a trough), the rock passes downwards into 

 the same sandy and siliceous limestones which form the summit of 

 the picturesque cretaceous hill of Olevano. Again, at Subiaco 

 (see fig. 35), the church of Maria della Valle is built on an inclined, 

 nodular, grey macigno with soft partings, which, covered by a mass 

 of unconformable and horizontal tertiary conglomerate, passes down- 



* An accident which injured one of my legs prevented my exploring the hilly 

 tracts east of Perugia and Assisi. But T could hear of no nummulites in the en- 

 virons, and the Museum of the University does not contain them. 



