ANNIVEKSAEY ADDRESS OF THE PRESIDENT. IxXXui 



A description of one section given by the author as seen between 

 Madrid and Burgos, before entering Molar, will suffice to give an 

 idea of the superposition of the beds. They dip 30° S.E. The base 

 consists of a few metres of arenaceous beds resting on the gneiss, 

 having in the middle a thin band of limestone. These are followed 

 in ascending order by a considerable thickness of limestones of 

 various qualities, succeeded by a thick mass of marls and argilla- 

 ceous limestone, and thin beds of limestone containing an irregular 

 tabular vein of manganese ; the whole being followed by the dilu- 

 vial gravels. In some places, as at Atalaya del Vellon, marly beds 

 are interstratified with the lower arenaceous beds. After describing 

 the general form and structure of the principal masses of this for- 

 mation, which has a general inclination of from 20° to 50° to the E., 

 N.E., and S.E., according to the great bend to which these beds have 

 been subjected, circling as it were round a central point, the author 

 notices the principal escarpments and ravines, and some of the 

 numerous and extensive caverns met with in this province. 



He then proceeds to describe the fossils of the formation. 

 These are very few, but, as he observes, sufficient to identify this 

 formation as the second group or Lower Chalk. The following are 

 the species found and described by Don Casiano : — Astarte striata 

 Sow. ; Area Cenomanensis, d'Orb. ; Mytilus Vemeuili, a new species 

 resembhng M. alternatus ; Lima cretosa, Duj.; Lima dichotoma, 

 Reuss ; Avicula pectinoides, E-euss ; Avicula Villanovana, a new spe- 

 cies ; Pecten tricostatus, Bayle ; P. quinquecostatus, Sow. ; Sjphceru- 

 lites squamosus, d'Orb. ; Hemiaster Fourneti, Desh. ; Nucleolites lacu- 

 nosi(s(?), Agas., in bad condition ; Area, new species, resembling A. 

 Tailleburguensis ; Terehratula, probably a new species. The author 

 also mentions other genera, of which he discovered fragments too 

 imperfect to enable him to give their specific denomination, as a 

 claw of a Crab, the cast of a Tilostoma, three species of Cardium, a 

 Cardita, Cyprina, Area, Mytilus, Modiola, two species of Ostrea, 

 several Rudistes, and two small Echinodermata. 



It may be here observed that the general faeies of this list, im- 

 perfect as it is, corresponds with the fact mentioned by Sir C. Lyell in 

 the last edition of ^ The Elements of Geology'*, that in the rocks of 

 the Cretaceous era in the south of Europe Ammonites are scarcely 

 ever found, and the genera Hamites, Turrilites, Seaphites, and perhaps 

 Belemnites, are entirely wanting ; while, on the other hand, genera 

 belonging to the great family of the Rudistes of Lamarck are gene- 

 rally abundant. 



Tertiary formation. — This forms one of the three great belts into 

 which the province of Madrid is divided, both geologically and geo- 

 graphically, extending from N.W. to S.E. Its thickness is consider- 

 able, but, owing to the effects of denudation, it is very variable ; 

 in some places, however, it is known to attain a thickness of about 

 340 metres without reaching the base. It is not a marine forma- 

 tion. The only fossils hitherto found are of terrestrial or freshwater 



^ ' Elements of Geology,' by Sir C. Lyell, 6th edit. p. 334. 



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