These mountains divide the peninsula into four regions: the narrow littoral on the northern coast; Aragon, Catalonia, Valencia, Murcia, and most of La Mancha, looking toward the Mediterranean; Almería, Málaga, and part of Granada and Cádiz in the south of Spain; and the vast region comprising the rest of the peninsula. The last-named is subdivided into four principal regions of importance historically. The Carpetana, or Carpeto-Vetónica, range in the north (more often called the Guadarrama Mountains) separates Old Castile from New Castile and Extremadura to the south, and continues into Portugal. The Oretana range crosses the provinces of Cuenca, Toledo, Ciudad Real, Cáceres, and Badajoz, also terminating in Portugal. Finally, the Mariánica range (more popularly known as the Sierra Morena) forms the boundary of Castile and Extremadura with Andalusia. Each of the four sub-divisions has a great river valley, these being respectively, from north to south, the Douro, Tagus, Guadiana, and Guadalquivir. Various other sub-sections might be named, but only one is of prime importance,--the valley of the Ebro in Aragon and Catalonia, lying between the Pyrenees and an eastward branch of the Iberian range. Within these regions, embracing parts of several of them, there is another that is especially noteworthy,--that of the vast table-land of central Spain between the Ebro and the Guadalquivir. This is an elevated region, difficult of access from all of the surrounding lands. Geologists have considered it the “permanent nucleus” of the peninsula. It is in turn divided into two table-lands of unequal height by the great Carpeto-Vetónica range. The long coast line of the peninsula, about 2500 miles in length, has also been a factor of no small importance historically. Despite the length of her border along the sea, Spain has, next to Switzerland, the greatest average elevation of any country in Europe, so high are her mountains and table-lands. [Sidenote: Disadvantageous effects of geography.]