ON THE TERTIARY FORMATIONS OF SPAIN. y 



classified by the author in three distinct groups or series. The upper 

 series is mainly calcareous, the intermediate gypseous marly, and the 

 lowest principally argillaceous. 



The upper series is 50-60 feet thick in the centre of the basin ; 

 none of the separate beds are above four feet thick ; they are chiefly 

 calcareous, but alternate with others of sand, marl and clay. The 

 lime contains a little silex, and nodules of ferruginous sandstone. In 

 some places it contains numerous remains of Limnceus socialise Pla- 

 norbis carinata and Paludina impura, all of which are still existing 

 freshwater species. In other places, as near Arevalo, the limestone 

 is more siliceous, and in proportion as the lime disappears, the result 

 is the production of a kind of semiopal and chalcedony, as in the 

 neighbourhood of Vicalvaro and Vallecas, in the basin of the Tagus. 

 All these characters agree with what geologists call "the siliceous 

 freshwater limestone." 



The middle group has a thickness of more than 200 feet. The 

 beds are generally marly, alternating with argillaceous beds, and all 

 filled with an extraordinary abundance of beautiful crystals of selenite. 

 In the lower portion of the gypseous series is often found a limestone 

 bed three feet thick abounding with Limnseus and Planorbis. This 

 limestone is not honeycombed like the former and contains but Httle 

 silex ; consequently it is not so hard or compact, and cannot be used 

 like the other for mill-stones. 



The thickness of the beds of the lower series has not yet been ascer- 

 tained. It begins with a thick bed of Nageljluhe, in some places six- 

 teen feet thick. This is nothing but an agglomeration of rounded 

 pebbles of various sizes joined together by a cement at times suffi- 

 ciently hard to be worked into hewn blocks. Below it is an argillaceous 

 bed, varying not only in thickness but in character j at times it is 

 pure white and compact, as in the vicinity of Palencia, where it is 

 used as a kind of fuller's earth for washing stuff's ; at others it is 

 bluish, mixed with marl, and contains an immense quantity of the 

 fossils above mentioned. Below these beds of clay are others of sand, 

 marl and clay alternating irregularly ; sometimes the nagelfluhe again 

 occurs of very moderate thickness, the pebbles being very loose and 

 forming a true gravel. All this would appear to show that when 

 these lower beds were deposited, there existed great currents of water 

 flowing in diff'erent directions. This is also proved by the isolated 

 remains of large pachyderms which are there found. The skeleton of 

 an individual of this kind was found a few years back near Sopefia, six 

 miles north of Valladolid, in the excavations made to open the canal 

 of Castille. Sufficient attention was not paid to these relics, but from 

 the examination of a tooth which was preserved, the author is disposed 

 to attribute them to the genus Mastodon. Near Paredes other bones 

 were found on a similar occasion, of which the author obtained a 

 femur and a molar tooth belonging to Mastodon angustidens of 

 Cuvier. It would therefore appear that the whole of the sedimentary 

 deposit which has filled up the basin of the Douro belongs to what 

 geologists have called the " gypseous tertiary freshwater." 



