1835.] Estramadura and the North of Andalusia. 351 



a rock which the miners term freylesca, formed of small 

 distinct fragments of talc or clay-slate, possessing a dark- 

 gray colour, with a structure resembling some species of 

 porphyry. It is more easily worked than the other rocks, 

 and is conjectured by M. Le Play to be connected with 

 the formation of the veins. The veins themselves are 

 formed of compact quartz, impregnated with cinnabar, and 

 a small quantity of native mercury. Sometimes the matrix 

 of the mineral is a black bituminous slate, which becomes 

 white by calcination. 



Notwithstanding the thickness of the vein, in consequence 

 of the good system of mining, its mass is extracted entire. 

 Frequently pieces of perfectly pure cinnabar are obtained. 

 A cubic metre (35*317 Eng. cub. feet) of the ore in a rough 

 state produces 325 kilogrammes (2 cwt. 11 lbs.) of mercury. 

 The mining is conducted by driving successive levels or 

 galleries, at different depths. The total depth of the pits 

 in May 1833 was 307 varas, (841 feet.) The annual product 

 of the mines of Almaden is 22*000 quintals (1078 tons.) 

 Hence, this spot alone furnishes twice as much mercury as 

 all the other mines together, in Carniola, Hungary, the 

 Palatinate, and Peru. 



Silver mines, according to tradition, were anciently 

 worked in Estramadura and the Sierra Morena. Those best 

 known are at Guadalcanal. In the middle of the seven- 

 teenth century silver was raised here and at Cazalla, from 

 the transition slate, mixed with sulphur, antimony, and 

 arsenic. Silver is also said to exist about Logrosan and 

 Zafra ; and M. Le Play heard that mines of this metal had 

 commenced successfully to the west of Pedroso. At El 

 Chantre a silver mine is still shewn, but nothing could be 

 detected among the debris but pyrites and galena. 



Lead is found abundantly, in the form of galena, in veins 

 in the stratified transition rocks. Defourcy found some 

 specimens to contain the following proportions of silver 

 and lead. 



Lead. Silver. 

 Cardosa near Llerana .... 793- - 000*63 



Los Pobres 752* - 000*47 



Truxillo 789- - 000-35 



San Calisto, Sierra Morena . . 630* - 000*30 



