561- Geological Society: — Prof. Agassiz on the polished surfaces 



others less so, being of great thickness. The fragments of the calca- 

 reous breccia are angular and of various sizes, and are cemented by 

 carbonate of lime. 



In the ravine of Cartala, protruded masses of trap, containing 

 veins of asbestos, amphibole, and porcellanite, are stated to have dis- 

 located the strata; an inconsiderable vein of trap is also described 

 as interposed between two beds of limestone. The slate clays 

 near the masses of trap, are said to be frequently of a green colour. 



At the eastern extremity of the chain, the limestone is overlaid 

 by beds of gypsum, containing masses and strings or small veins of 

 native sulphur. 



There is no doubt that mines in this mountain chain were worked 

 by the Romans. The ore is generally found in nests or masses of 

 inconsiderable size ; also in veins and branches of limited extent in 

 any constant direction, crossing each other, and forming almost 

 always communications between the nests. Mr. Lambert is there- 

 fore induced to consider these metallic accumulations as of contem- 

 poraneous origin with the limestone. At the mine of Arnafe, on 

 the western edge of the Sierra, the ore occurs between two beds of 

 limestone, having the same direction east, 20° north, and dipping 

 with them 80° to the N.E. It is one foot thick, and is accompanied 

 by clay. The same agreement has been found in Santa Rosa, Santa 

 Catalina, Cruzados, Trinidad primero, and in all the mines situated 

 upon the western declivity, looking towards Berja. 



In the Loma del Sueno, and the interior parts of the Sierra, where 

 the beds incline only 20° to 30°, but frequently exhibit great dis- 

 locations, which change their position entirely, and often form 

 crests, fissures, and hollows filled with argillaceous substances, are 

 found the greatest masses of ore, lying between the beds, and con- 

 forming to all their modifications. Fluor almost always accom- 

 panies the galena. 



One level has been carried nearly 600 yards in length, from the 

 bottom of a precipice of nearly equal altitude, in order to under- 

 mine the rich deposits on the edge of the Loma del Sueiio, but 

 hitherto nothing has been met with but comjoact and slaty lime- 

 stone. Mr. Laml)ert therefore infers, that the ore is more super- 

 ficial, and he adds, there is no instance of its having been found at 

 a greater depth than 200 yards from the surface. 



The lower parts of the fissures which traverse the limestone, are 

 frequently filled with fragments of ore enveloped in a red earthy 

 soil, and associated with angular as well as rounded fragments of 

 limestone. In the alluvial detritus of the ravines, and the dry 

 deltas at their mouth, fragments and masses of ore have been ex- 

 tracted, often in considerable quantities, and at the Pecho de las 

 Lastras to the extent of 100,000 tons. 



In the limestone mountains which stretch westward from the 

 Sierra de Gador to Marbella, within forty miles of Gibraltar, lead 

 ore is found in variable quantities, but not so abundantly as in the 

 Sierra de Gador. 



In conclusion, Mr. Lambert observes, that the improvident me- 



