Professor Htmsmann on the. Geology oj the Apennines. 279 



black siliceous slate, and scales of silvery mica. The cement 

 is present in small quantity, and is even sometimes wholly 

 wanting, in which case the portions of quartz lose the granu- 

 lar form, and constitute a continuous mass, making a transition 

 from grey wacke to quartz rock. At other times it passes into 

 clay-slate and into compact limestone. 



jClay-slate, flinty-slate and talc-slate are next noticed ; the 

 latter occurring more frequently and in larger masses, passing 

 on the one hand into clay-slate, and on the other into chlorite- 

 slate. When mixed with quartz it forms the " saxuin forna- 

 cum," or Gcstellstein (a kind of oven-stone). This rock was 

 noticed by Saussure * and St. Fond f , between Genoa and Fi- 

 nale, alternating with compact limestone and clay-slate, and 

 is hence inferred to be of secondary formation, as is likewise 

 the gneiss observed by Saussure % near Voltri. 



Compact limestone, which is so important in the geological 

 structure of the Alps, is not less so jn that of the Apennines. 

 It alternates with grey wacke and clay-slate; in some places 

 passing into those rocks. Its colours are various, but grey is 

 the most common. It contains but few organic remains; a 

 rare specimen of an ammonite was met with by Micheli§, 

 which is preserved in the collection of Professor Targioni at 

 Florence. 



When the compact limestone is mixed with quartz and 

 mica, it constitutes the pietra forte, much used at Florence 

 and other places for paving the streets. 



The transition rock of most interest in these mountains is 

 the brecciated limestone. Some important observations upon 

 this rock have been made by Brochant ||. It is apparently 

 composed of fragments of limestone, of various shapes and co- 

 lours, united by a calcareous cement, sometimes mixed with 

 talc, clay-slate, and other matters. Its colours are strongly 

 contrasted, and it has sometimes the character of the beautiful 

 African breccia. In other instances it approaches the antique 

 Cipullinc marble. Where the nature of the fragments does 

 not differ greatly from the cement, there takes place a transi- 

 tion into compact limestone, or marble, which was noticed 

 mar Carrara, where the brecciated marble alternates with the 

 compact. 



Professor I Iausmann describes the appearance of the brec- 

 ciated limestone of the Apennines, as rough, and traversed by 

 numerous fissures, which are particularly conspicuous where 

 the cement is softer than the included fragments, and being 



* Voy. dans les Alps. vol. iii. p. 1G7. t Anna!, du Mas. vol. xi. p. '22J. 

 \ Voy. <lan< les Alp., vol. iii. p. 1 .">!). § Ferber's Bride, p. 327. 

 || Joiir. de: Mines. N. 137- p. 321. 



acted 



