214 I. Bowman — Physiography of the Central Andes. 



tnre in the gorge wall above and below the contact. The 

 sandstones and conglomerates weather with typical Grand Can- 

 yon effects, — an alternating series of vertical scarps and sloping 

 talnses characterizing the upper part of the section, while the 

 lower part is irregularly dissected, presenting every complex- 

 ity of slope arrangement. Above Chacarilla the piedmont 

 deposit thins out and disappears towards the edge of the 

 plateau. 



The distance from the crestline of the iindes (east of the 

 Chacarilla mountains) to the seacoast is approximately 80 

 miles. At Cerro Gordo a distinct block rises above the pied- 

 mont slope, breaking its continuity for several miles, and again 

 directly west of the Pique pumping station, a granite block 

 juts sharply above (500 ft.) the general level. In the well-nigh 

 absolutely arid climate of the region the but partially rounded 

 edges of these blocks reflect their original outlines with remark- 

 able distinctness. The upper surface of the Pique block (3,500 

 ft.) is flat to gently rolling, only rounded knobs of slight 

 extent surmounting the generally even surface. The pene- 

 plained character of the block appears from the general even- 

 ness of its surface as developed on rocks of diverse structure 

 and hardness. The western part of the block is composed 

 of sandstones, the eastern of a fine-grained resistant igneous 

 rock, both reduced to a common level. Toward the eastern 

 margin the surface becomes slightly dissected, long fans of 

 waste choking the mouths of ravines and stretching out over 

 the saline crust that forms the salars, the stark desert places 

 of the province of Tarapaca. Such dissection is, however, 

 decidedly inconsequent on the whole ; the ineffective drainage 

 results, even on the ravine sides, in a waste cover so deep that 

 only here and there are rock outcrops distinguishable. The 

 edge of the block is, therefore, clearly limned as a strikingly 

 even and abrupt escarpment, but imperfectly dissected by the 

 feeble, intermittent streams. 



The view from the Allianza nitrate station of that part of the 

 now warped and uplifted peneplain which includes the Chaca- 

 rilla mountains is represented in the rough sketch in fig. 10. 

 The summit of the upwarped plateau retains the general charac- 

 ter here depicted, southward beyond Santa Fe in the Loa 

 Yalley (see general map of Chile). At Calama the old 

 initial surface was again observed as a tilted block south of the 

 oasis of that name, where it stands out with unfailing clearness. 

 This baseleveled surface, with whose identification, broad 

 aspects, and detailed character at critical localities we have 

 thus far been concerned, has thus been observed to occur for 

 over one hundred miles, from Calama to Tarapaca. It will be 



