The morphological features of the Patagonian Andes begin at 36 deg. S. lat.[53] The edge of the Cordillera, in the Malargue depression, below 35 deg. S. lat., still presents the typical scenery of the central Andes. The dejection-cone of the Atuel resembles that of the Mendoza. The fringe of torrential deposits, distributed in cones over which the waters spread, is due to the rapidity of the disintegration of the rocks in a desert climate. Keidel has pointed out the part played by the summer rains in transporting mobile elements, which the water drops as soon as the slope diminishes; the amount of precipitation being too slight to permit the formation and spread over the plain of a regular network of streams. From the Rio Grande onward the dejection cones disappear. The streams tend to become permanent, and sink into narrow valleys. The summer rains cease, and the water produced by the melting of the snows has only a feeble capacity for transporting stuff. The soil of the Cordillera is protected by a denser vegetation. The first thickets of _molle_ appear in the valleys, the first scattered cypresses on the slopes, at the Rio Agrio, a tributary of the Neuquen. Then the forest invades the mountain: at first, from 38 deg. S. lat. to 39 deg. 30' S. lat., a resinous forest of araucarias. At length, at Lake Nahuel Huapi, the forest assumes the general appearance which it has as far as the Magellan region. It is chiefly made up of different kinds of beeches. The _coihue_ (_Notofagus dombeyi_) is the most conspicuous for about three quarters of a mile, rising above an impenetrable undergrowth of bamboo. Higher up the domain of the _lenga_ (_Notofagus pumilio_) extends as far as the fringe of the Alpine forests. The forest does not reach the eastern limit of the lakes. In the sub-Andean depression it is reduced to thickets of _nirre_ (_Notofagus antarctica_) and _mayten_ and clumps of _calafate_ (something like myrtles).