ORIGIN 



289 



planes. Within the finest loess one sees in vertical sections lenticular areas 

 of finer or coarser pebbles. Small aprons of talus at close and fairly reg- 

 ular intervals border the river walls at their bases (plate 35, figure 2). 



Seen from the heights about the valley, not only is the surface of the 

 formation notably horizontal, but several stages of lower and parallel 

 planes produce sharply delimited shelves wherever the river has opened 

 the formation in sections. The upper layer and some of the lower ones 

 show a rich brown color, and on nearer approach are seen to be colored 

 with soft hematite. As one looks to the southward beyond the formation 

 toward the distant Sierra Nevadas, one sees rising at their base the black 

 mass of the mountain of hematite at Alquife,* and it is difficult not to as- 

 cribe a common source to it and to the hematite of the Guadix formation 

 in an earlier ferruginous deposit situated higher up and in the Sierras 

 themselves. The color effect in the general view from below Diezma is un- 

 usually fine, the hematite layers standing out in the dissected valley floor 

 like pencil lines, with the black iron mass of Alquife and the white dolo- 

 mite of the Alcohorra (each capped by a Moorish castle) sharply outlined 

 against the gray background of the Sierra Nevadas. Where the Farde 

 has cut its broad valley, patches and strips of green appear beneath the 

 diversified and picturesque "bad land" topography which surrounds 

 them. The labyrinth of loess columns, eaten into by the sudden rains, 

 have been excavated locally to furnish homes for a large proportion of 

 the peasant population in the district (see plate 36). Plate 35, figure 1, 

 shows the abundance of irregular boulders upon the surface of the forma- 

 tion where it borders upon the Sierra Nevadas. 



Origin of the Formation 



The Guadix formation appears to be largely a torrential deposit of 

 material derived from the neighboring Sierras, with local characteristics 

 restricted to the individual valleys of the Genii, Darro, and Farde, and 

 dependent on the rock material which is in place near the headwaters of 

 those streams. The material is coarser near the borders of the formation, 

 while loess and floating material, such as roots and brush, are more char- 

 acteristic of the central and presumably quieter areas. To account for 

 the almost perfect horizontality of the beds within the central areas, it is 

 necessary to assume the former existence of at least temporary lakes 

 within the valleys, while the lenticular forms of the pebbly material in 

 the sections indicate that streams once coursed over the floor of material 

 below. Some part has undoubtedly been taken by the wind in depositing 

 the formation, since it is active today in transporting the lighter ma- 



* See an article by the author treating of the iron mines at Alquife. 



