346 Colonel Silvertop on the Lacustrine Basins of' 



The little valley of the Guardal, between Benamaurel and 

 Castillejos, has a varying breadth and form. At times it is re - 

 duced to a narrow slip of land, confined on one side by a high 

 escarpment, and on the other by step-like platforms of the 

 marls successively becoming more elevated as they recede from 

 the rivulet ; at others it expands into little circular basins, from 

 a quarter to half a mile broad. The course is nearly north and 

 south; the Distance between the two last-mentioned villages is 

 about ten miles. 



From Castillejos to Huescar, a distance of about twelve miles, 

 the tract exhibits appearances identical with those lately de- 

 scribed ; but on approaching the latter town, the gypsiferous 

 marl deposit is concealed under a gently inclined plane of allu- 

 vium, of a sandy character and reddish colour. This extends 

 to the base of the first low ridge of secondary limestone, which 

 has been stated to form the northern boundary of the basin, 

 and which, a few miles still farther north, rises into a series of 

 elevated chains and magnificent mountains, the highest of which 

 is known by the name of La Sagra. 



It appears, therefore, in crossing this basin from south to 

 north, or from Baza to Huescar, that it is entirely occupied by 

 a deposit of gypsiferous marl in horizontal strata, whose total 

 thickness may perhaps be estimated at between 300 and 400 

 feet, judging from the height of the escarpment at Benamaurel, 

 and the depth to which the sulphur workings have been carried 

 in a hollow of denudation at a much lower level than the surface 

 of this formation near the last named village. 



The gypsum, so abundant in this deposit, is almost univer- 

 sally in wedge-shaped separate pieces, many of which are often 

 joined together, and form irregular masses of the size of a large 

 cannon-ball. These are imbedded in great profusion in the 

 marl strata, which generally are from 3 to 4 inches thick, but 

 vary from 1 to 6. In other places these strata are studded 

 with small facettes of gypsum, and an instance rarely occurs 

 where it is not visible in one form or the other. Its structure 

 is universally laminated. 



I shall now proceed to say a few words upon the appearances 

 presented along the line of road which passes over the eastern 

 portion of this basin. About sixteen miles from Baza, and on 



