Its general trend is east and west; towards the south it sinks precipitously, and on the north it descends with a somewhat moie gentle slope towards the longittidinal valleys of the Tormes and Alberche which separate it from another rugged mountain range, forming the southern boundary of the paramera of Avila.
The principal rivers are the Alberche and Tietar, belonging to the basin of the Tagus, and the Tormes, Trabancos and Adaja, belonging to that of the Douro.
The principal right-hand tributaries, besides the Gallo and Zezere, are the Jarama, descending from the tableland of New Castile a little below Aranjuez, the Alberche and the Tietar, which collect their head waters from opposite sides of the Sierra de Gredos, and the Alagon, from the rough and broken country between the Sierras de Gredos and Gata.
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