and Geognostical Constitution of Spain. 273 



posite oF Jead-glance in the Sierra de Gador, which afforded, in 

 the year 1828, 600,000 cwts. of lead, is distributed in masses 

 (putzen), in a limestone which may be referred to the oldest 

 transition-rocks, and the rich mercury mines of Almaden, are 

 contained in clay-slate. 



The secondary rocks also assist in forming the principal 

 Spanish mountain chains, but in a different manner. They 

 ascend to a great height on the Spanish side of the Pyrenees, 

 even some of the highest summits are of secondary rocks. The 

 western continuation of the Pyrenean chain consists, in the Bis- 

 cayan provinces, principally of secondary rocks ; and it is pro- 

 bable that the lofty limestone mountain ridges which separate 

 Austurias from Leon, is a continuation of the Biscayan second- 

 ary formation. On both sides of Somosierra the primitive rocks 

 are skirted by those of the secondary class, but they are far 

 from the middle and higher parts of the mountain chain. When 

 we follow the road from Madrid to Andalusia, we meet with 

 secondary rocks near the transition clay-slate of the passes of 

 the Sierra Morena, but we must descend very low on the south 

 side before we meet with similar rocks. The high mountains of 

 Jaen are formed of secondary rocks. In the northern vorge- 

 berge of the Sierra Nevada, between Granada and Guadiz, 

 there are secondary deposites, which are not^ however, so con- 

 siderable and extensiv'C as to reach to the higher ridges. Also 

 in the vicinity of Malaga new secondary rocks lie on the foot 

 of older mountain masseS; and ridges of secondary rocks extend 

 from the hills of Ronda towards the southern extremity of Spain. 

 The wonderful isolated Rock of Gibraltar is also principally 

 composed of new secondary rock. The distribution of the rock 

 is not confined to the immediate vicinity of the higher mountain 

 chains, but it extends from the one to the other, rises or falls in 

 the intermediate spaces, and forms in this way the widely ex- 

 tended high table land. 



The most important of the Spanish secondary rocks are the 

 following, viz. variegated sandstone and marl, grypliite limestone 

 and the white limestone or Jura limestone. The first of these 

 exhibits the same relations as in Britain, where it is known un- 

 der the name New Red Sandstone, or Red Marl. The shell 

 limestone, which, in Germany, is enclosed between Werner's va- 

 riegated sandstone, and the younger variegated marl forma- 



JANUAKV .MAUCII 1830. S 



