40 THE OASES OF THE NORTH-WEST 



the upper stratum of a considerable series of continental 

 deposits which lie on the Paleozoic crystalline rock of 

 the Andes. I They chiefly consist of red sandstone and 

 coloured marls, which crop up here and there through 

 the alluvial covering and give the landscape a rugged 

 character, worn by water and wind. There is no trace 

 of humus : nothing to soften the vivid colours of the 

 rock. Bodenbender, to whom we owe the first general 

 attempt to classify the series, points out the import- 

 ance of distinguishing the different strata in connection 

 with the question of water supply and the conditions 

 of human life. 2 A complete geographical study would 

 have to follow the geological description in detail. 

 In places — on the eastern edge of the Sierra de los 

 Llanos — the fine modern clays are in contact with 

 the granites of the hills and form above them a thick 

 bed that is rich in fresh water. In other places — south- 

 westward of the Sierra de la Famatina, as far as the 

 Bermejo — the outcrop is of red sandstone only. The 

 tablelands of Talampaya and Ischigualasta, which are 

 cut across by the gorges of the tributaries of the 

 Bermejo, form one of the most conspicuously desert 

 regions in the whole Republic. Wherever the gypsif erous 

 marls of the Calchaqui are near the surface, the springs 

 are saline. The undulations of the impermeable rocky 

 substratum bring to light the water that gathers in 

 the alluvial beds. Thus the streams which come down 

 the Famatina range in the west disappear in the alluvial 

 beds on the fringe of the Sierra, but re-appear presently 

 in the oasis of Pagancillo. 



J This series, stretching from the Permian to the Tertiary, also 

 includes, especially in the region of the sub-Andean chains, on the 

 fringe of the Chaco, a number of marine strata (see Bonarelli, Las 

 sierras suhandinas del Alto y Agnaragiie y los yacimientos petroliferos 

 del distrito minero de Tartagal (" Ann. Min. Agric," Seccion Geologia, 

 Mineralogia, y Mineria, viii. No. 4 : Buenos Aires, 1913). 



» G. Bodenbender, Parte meridional de la Provincia de la Rioja y 

 regiones limitrofes (Ann. Min. Agric, Seccion Geol., Minerol., y Mineria, 

 vii. No. 3 : Buenos Aires, 191 2), 



