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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 8, 



3. On the Geology of Spain. By Don Joaquin Ezquerra del 



Bayo. 



[Communicated by Sir R. I. Murchison, V.P.G.S.] 



In order to give a general idea of the geological constitution of our 

 country, it may be considered as divided into three principal divisions, 

 viz. the Crystalline or Gneissoid formations ; the Transition forma- 

 tions ; and the Secondary. The first predominate almost exclusively 

 in the western portions (not including Portugal), in the whole of the 

 ancient kingdom of Galicia, and extend through Astorga, Zamora, 

 Salamanca, Placencia, Caceres, Me'rida, Llerena, Aracena, and Rio 

 Tinto, to the north of Seville and to the neighbourhood of Itahca, 

 the birth-place of the Emperor Trajan, now called Sancti Ponce. It 

 must however be observed, that as vet, for want of detailed observa- 

 tions, we have no definite lines to mark the limits of the three for- 

 mations above mentioned. We can only say that the gneiss rocks 

 occupy about a fifth of the surface of the soil, extending longitudi- 

 nally from north to south, but throwing out, as it were, ramifications 

 towards the east. 



These gneiss rocks are probably secondary or piimaiy formations, 

 altered by the plutonic rocks which have penetrated them. These 

 are generally ordinary granite, more or less coarse-grained, and some- 

 times traversed by veins or dykes of porphyritic granite. Only at 

 the northern extremity, ^iz. between Aracena and Llere'na, in the 

 villages of Zufre and Santa Olalla, is a great syenitic outburst visible. 



The most important of these granitic ramifications to the east is 

 that which passes by the Sierra de Gridos, Sierra d'Avila, and the 

 Guadarrama, to Somo Sierra, in a direction from south-west to north- 

 east. The great granitic outburst of Tnixillo and of the mountains 

 of Toledo does not extend so far to the east. A third, which is not 

 so well marked as the other two, i. e. does not appear on the surface 

 with the same continuity, is that which has probably given its present 

 form to the Sierra Morena. It terminates at Linares, in the pro^dnce 

 of Jaen. 



The gneiss rocks in Spain do not generally abound hi metalliferous 

 deposits. There are some however of considerable importance. All 

 the copper deposits of the district of Rio Tinto occur in talcose schist, 

 in the vicinity of the granite. The famous mines of Guadalcanal 

 and of Cazalla (now exhausted) are opened in chloritic schist, not far 

 from the syenitic outburst. The rich argentiferous veins lately dis- 

 covered at Hiendelencina, in the province of Guadalaxara, traverse 

 the real gneiss, and are also not veiy distant from the granite of 

 Somo Sierra. 



The plutonic rocks themselves are still less rich in useful metals 

 compared ^^^Lth their great development. The most important deposit 

 in a rock of this character is the great system of lead and copper veins 

 in the district of Linares, both for the abundance and excellent quahty 

 of the minerals. The granitic rocks in the neighbourhood of Mon- 

 terey in Galicia contain a small quantity of tin, as well as those of 

 Carbajosa and Carbajoles, near Zamora, on the frontier of Portugal. 



