The Cretaceous forms the broad plateau of the Lora on the southern front of the Cantabrian mountains north-west of Burgos and extends southward and westward into a Cretaceous isthmus in the northern side of Miocene "Straits of Burgos." An upfold brings it to the surface again in the island-like Sierra de Atapuerca on the south side of the "straits" toward the Montes de Oca. From the scarp of the Urbion the Cretaceous dips gently south ward and Upper Cretaceous limestones form small, bare, fault bounded plateaux sharply contrasting with the pine-clad slopes of the lower Cretaceous and appearing at the surface not only on the margin of the zone but in the upfolds of small radius among the Tertiaries of the Domo, at Burgo de Osma, Sovia and else where.
South of the Jalom river beyond the Paramess de Molina the border of the Meseta is formed principally of Jurassic limestones and marl commonly capped by horizontal limestones of the Cre taceous and forming a series of high plains rather than mountains in which the muela, or molar-tooth, summit is typical. The differ ent alineations, however, are known as the Serrania de Cuenca, Montes Universales, and Sierra de Albarracin.
Tertiary.—Deposits of Tertiary age cover rather more than a third of Spain. On the Meseta the Tertiary formations were laid down in the basins of Old and New Castile and in the minor sys tems of Castello Branco (Beira Baixa), Badajoz, and others of the Tagus and Guadiana valleys. In the west arkose grits of Lutetian date from a broad, monotonous plain in the provinces of Zamora and Salamanca and the old Tertiary (Palaeogene) beds appear also in the east near Lerma and in the plateau of Sovia. Elsewhere the outer deposits of Palaeogene are insignificant. The continental Miocene, unconformable on the Palaeogene, con sists of fine-grained materials laid down within the basins of the Palaeogene, and the Cretaceous to which it is unconformable had been folded in the margins of the basins, by rivers (Tartonian), brackish ponds (Sarmatian) and in marshy ponds (Pontian). In spite of stratigraphic discontinuity the forms of the Miocene relief are constant and characteristic. The type form is the table land (mesa), with its flat upper surface of the limestone cap (paramo), its slope of marl (cuesta), and its sands or clays of the lower slopes forming plains (elanuras, canapin as, campos).
As the erosion advances the worn table-lands appear as truncated pyramids or form low mesas capped by the beds of harder marl. Finally great stretches of plain are formed on the level of the Tor tonian on lower Sarmatian. Space will not permit a full descrip tion of the Tertiary formations elsewhere. The Eocene marine strata are developed in the basin of the Ebro and Miocene deposits occupy some small tracts especially on the coast of Valencia al though most of the sandy Tertiary rocks of the latter district are Pliocene. In the Baetic depression the marl of the Tertiary rocks of whatever level are of great importance, supplying the rich soil of the Cijarafe olive groves west of Seville and of the vineyards of Jerez.
Quaternary deposits spread over about a tenth of the country. The largest tract of them is to be seen to the south of the Canta brian mountains, although another but little smaller flanks the Sierra de Guadarrama and spreads out over the great plain from Madrid to Caceres.
From the rivers Douro, Tagus, Guadalquivir and Ebro, E. H. Pacheco has described recently four fundamental terraces at heights of 3o, Ioo, 200 and 33o ft., which are fairly constant within limits of 4-33 ft. from the higher terraces, and he has commented on the absence of terraces on the Spanish section of the Guadiana river. The highest terrace is of late Pliocene date and to it are referred the famerus rafias, extensive platforms of coarse detritus high on the northern front of the Montes de Toledo. The others seem to be related to the terminal moraines of the Pleistocene glaciation with which, in some cases at least, they are continuous. There moraines are found as low at 2,300 ft. on the Sierra de Estrella (one of the westernmost sierras of the central cordillera) ; and the topography of the Picos de Europa (of the Cantabrian mountains), the Sierra de Guadarrama and the Sierra de Gredos (of the central cordilleras), the Sierra Nevada, and the Iberian ranges from the Demanda to Moncaya has been modi fied to some degree by glaciation. But the centres of glaciation in each of these cases were relatively small, and the action local.
Only in the Pyrenees are the glacial phenomena of real topo graphical importance. The terraces, on the other hand, are of first importance, making irrigation possible in areas otherwise arid.