M., and includes the greater part of the vast plateau of Old Castile, between the watersheds of the Cantabrian Mountains, on the north, and the Guadarrama, Gredos, Gata and Estrella ranges, on the south.
The Triassic system is well developed in the north of the peninsula along the Cantabrian chain and eastwards to the Mediterranean.
The lower members of the Cretaceous series include an important fresh-water formation (sandstones and clays), which extends from the Cantabrian coast through the provinces of Santander, Burgos, Soria and Logrono, and is supposed to represent the English Wealden series.
The largest tract of them is to be seen to the south of the Cantabrian chain; but another, of hardly inferior extent, flanks the Sierra de Guadarrama, and spreads out over the great plain from Madrid to Cceres.
The greater part of the interior of Spain is composed of a table-land bounded by the Cantabrian Mountains in the north and the Sierra Morena in the south, and divided into two by a series Central of mountain ranges stretching on the whole from east Table-land to west.