340 Colonel Silvertop on the Lacustrine Basins of 



broken barren-looking country. From Diesma to Baza, the 

 road is within the limits I have assigned to the basin under 

 consideration. 



On approaching Baza by this line of road, or from the west, 

 there is a long descent, the upper part of which exhibits on 

 each side a series of horizontal strata of compact limestone, 

 filled with paludinae, which, at a short distance towards the left, 

 forms a bold escarpment about seventy feet high, resting upon 

 marl, and bordering the lower and more central portion of the 

 basin. The same limestone, with its characteristic univalve, 

 also forms a low escarpment contiguous to the road, for a short 

 distance during the descent. The strata are from three inches 

 to a foot thick, and as near as possible horizontal, but others 

 were observed which had a thickness of four and six feet. The 

 limestone is of a muddy-whitish colour, its fracture smooth and 

 even, and in large fragments inclining to the conchoidal. During 

 the descent, the road is at times confined on the right-hand side 

 by an earthy marly embankment, in which large rolled masses 

 are seen of the same limestone, remnants in all probability of an 

 extensive bed of this rock which has now nearly disappeared. 



This locality is interesting to the geologist, as it affords a 

 proof of the superposition of the compact paludina limestone, 

 on the deposit of gypsiferous marl, which occupies so large a 

 portion of the basin of Baza, and which will be immediately the 

 subject of consideration. It is, however, the only point in this 

 basin where such limestone, as far as I have had an opportunity 

 of observing, can be seen ; but as a similar superposition will 

 be shewn to exist in the basin of Alhama, where a compact hme- 

 stone, characterised by the same paludinae, rests upon a thick 

 bed of gypsiferous marl, I am induced to consider the subjacent 

 beds in each, although differing in some points, to be identical, 

 and of similar origin. 



The extensive basin near Baza, in which these beds have been 

 deposited, is confined, towards the south, by the high ridge of the 

 transition i?) limestone, called the Sierra de Baza, which has been 

 stated to extend from Guadiz to the former town ; towards the 

 north it is bounded by the still more elevated mountains of 

 Huescar, formed of secondary nummulite limestone ; and to- 

 wards the east and west, in a more irregular manner, by lower 



