350 M. F. Le Play on the Geology of [May 



Corresponding to Ca. C + (Mg. /) C * 



Over the shell limestone is superimposed, at Cordova, an 

 argillaceous formation with rolled flints, which has obvi- 

 ously been transported thither as in Old Castile, Murcia, 

 Cape Palos, Marbella, and is considered as indicating a 

 third epoch in the tertiary series. At Badajoz similar 

 appearances present themselves, in the form of conglome- 

 rates, with flints, rising about 200 feet above the level of the 

 Guadiana. The fragments of conglomerate generally consist 

 of quartz, greywacke, slate and large flints. In the Rio 

 Gargaliga, reddish quartz appears ; the low plains of Serena 

 and Guadiana consist of fine silicious sand ; the hills in the 

 neighbourhood of the Guadiana are covered by clay, with 

 or without flints, renowned for its fertility, and termed in 

 the country tierra de barros. In addition to this formation, 

 numerous more recent disintegrations are observed in dif- 

 ferent situations, deriving their origin from atmospheric 

 influences. 



Minerals. — Estramadura contains a vast variety of metallic 

 minerals, which, if properly employed, would raise this 

 district to the first distinction. 



Mercury is found in large deposits in the form of cinnabar, 

 and native mercury occurs in the hill upon which Almaden is 

 built. The veins are parallel, almost vertical, and are distant 

 about sixty-five feet from each other. Their mean breadth 

 is about twenty-six feet, but sometimes the absolute dia- 

 meter is double this measurement ; the depth at which they 

 are worked is about 820 feet. One of these veins is termed 

 San Diego a levante, and the other San Francisco a levante. 



The rocks which the veins traverse are principally quartz 

 and clay- slate. At the south-west, of the first vein, there is 



* Magnesian limestone very often occurs in alternations with porphyry. In 

 Durham, breccia is connected with the extensive dolomitic beds ; and in Berwick- 

 shire I have described it (Loudon's Mag. of Nat. Hist. v. 627.) as alternating 

 with claystone-porphyry. Analysis shewed its composition to be, 



Carbonate of lime . . 49*6 

 Carbonate of magnesia . 44* 



Silica 4- 



Peroxide of iron ... 1*2 

 Alumina 1* 



99-8 



This is, abstracting impurities, = Ca. C -f- Mg. C. — Edit. 



