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 Cactus appears again upon the eastward-facing slopes, and one looks down over them into the fertile valley floor, where wheat and barley and corn are produced, upon the smooth-con- toured lower slopes and the terraced floor of the valley itself. It isa very pleasant landscape that is spread out to view.

West of the Cuesta del Obispo one enters a broad, waste- strewn valley floor after descending a steep and in places rocky trail from the pass. After crossing this broad alluvium-filled depression and a second narrow range one comes out upon the plain of Tintin, where the trail forks, one branch going west and southwest to Cachi, a town on the floor of the deep Cal- chaqui valley, and the other branch turning abruptly north to Payogasta and Poma. It was the latter that we followed, trav- ersing the dry, waste-strewn plain in the middle of a hot after- noon when clouds hung over the Sierra de Tintin on our left hand as well as on the distant Cordillera. The plain of Tintin is covered with cactus and desert shrubs of many varieties. Figure 98 represents the structure of the wood, and Figure 97 the field situation of the chief columnar cactus, the so-called cardén. It is valuable for rafters and in making doors and door frames, window frames, and parts of outbuildings. We are here far above the forest and in the zone of low winter tempera- tures; but the cactus continues its scattered growth all the way up the valley and on the lower slopes of the main mountain wall to surprisingly high elevations. I found it up the valley of Peias Blancas, almost a day’s journey from Poma, at an elevation of nearly 13,500 feet. It was growing chiefly upon the southern (warmer) wall of the valley, partly on lava flows, partly on the coarse débris washed or rolled down from these flows on the intermediate slopes of the valley. It is here sub- jected to almost nightly frosts for a part of the year.

in the high mountain country east of Iquique beyond the Cordillera Sillilica, where there are nearly six months of cold weather with severe frosts at night and often violent hail- storms by day, with some snow occasionally.
 * found similar forms at elevations exceeding 13,000 fect