338 Colonel Silvertop on the Lacustrine Bas'ms of 



of between 31,000 and 12,000 feet above the level of the sea. 

 Contiguous to the line of road, lower hills of transition-slate 

 and limestone are continually observed, and the latter, which lies 

 upon the former, constitutes an irregular line of hills bordering 

 the hollow towards the north, but these are immediately suc- 

 ceeded in the same direction by a continuous ridge of a secondary 

 nummulite limestone. This ridge ceases near a village called 

 Diesma, eight leagues from Granada. 



Between Diesma and Guadiz, an ancient city ten leagues 

 from Granada, the country begins to open out into that exten- 

 sive area, surrounded by high ridges and lower ramifications, in 

 a part of which, near Baza, I observed one of the beds in ques- 

 tion, resting upon gypsiferous marl. To the left or north of 

 the road in the intervening tract, a pretty even surface of table 

 land extends from near Diesma, towards the central portion of 

 this area, and often presents long slopes to different ravines 

 which intersect it, and an abrupt high escarpment to the valley 

 of Guadiz, exhibiting a mass of earthy calcareous marl, with fre- 

 quent beds of gravel, and horizontal strata of indurated conglo- 

 merate, whose cement is also calcareous. On the approach to 

 Guadiz, and between the road and the base of the primitive 

 chain towards the south, the ground presents evident proofs of 

 the overwhelming action of torrents, which at some remote pe- 

 riod have rushed down from these elevated mountains, and 

 furrowed it into ravines of great magnitude and depth. In 

 the .vicinity of Guadiz, argillaceous conical hillocks, at times in- 

 sulated, at others in little groups, and often so numerous and 

 thickly clustered as to resemble at a distance an immense en- 

 campment of tents, present views of most singular appearance. 

 A deposit of a marly, gravelly, argillaceous nature, appears to 

 have filled up all this portion of the area, upon which water in 

 a state of violent agitation, and exerting its power according to 

 the different resistances offered by such a heterogeneous mass, 

 has given to its surface so curious a variety of form, and by a 

 consequent great denudation, scooped out the Valley of Guadiz. 

 The upper portion of this deposit, as may be seen near the end 

 of the ridge or Sierra of Diesma, has the appearance of being 

 the result of the destruction of calcareous rocks ; whilst the lower 

 part, constituting the Valley of Guadiz, is of an argillaceous 



