Baza and AUtama. 79 



The superior part of the ridge consists of earthy marl and 

 horizontal strata of soft marly limestone, which hardens on ex- 

 posure to the atmosphere, and is used for building, alternating 

 with others of a more sandy nature ; and one stratum was ob- 

 served of a hard compact sandstone, a foot thick. Other strata 

 of the marly limestone intervening between the above and the 

 bed of brown coal, are coloured by carbonaceous matter, and full 

 of paludinaj. 



There appears to be a direct analogy, with respect to orga- 

 nic remains, between this deposit and the superior marly lime- 

 stone observed along the summit of the ridge between Cacin 

 and Alhama. The carbonaceous matter in the former is of 

 course of local occurrence. 



In proceeding from Arenas up this ridge, to its confines with 

 the primitive district, by the road which leads to the Puerto de 

 Competa *, the fii*st part of the ascent consists of earthy marl, 

 with horizontal strata of the same substance, or between this 

 and a coarse limestone, in an indurated state. I also observed 

 some masses of fine quartzose sand, similar to that above no- 

 ticed, but no appearance of the brown coal. The line of road 

 crosses the ridge diagonally ; near the mountainous district it 

 becomes entirely formed of a mass of gravel, crowned at times 

 by a thick stratum of reddish-coloured indurated conglomerate, 

 and this deposit -f- is observed to extend for a considerable dis- 

 tance in the form of an inclined band, covered with a forest of 

 pines, between the line of the primary rocks and that part of 

 the basin under consideration between Arenas and Jayena. 



The few remaining observations refer to this tract. The 

 road from Arenas to Jayena crosses over the little ridge last al- 

 luded to, at a short distance above the point where the two 

 streams, which may be said to bound it, unite, and descends to 

 that whose banks were stated to exhibit a series of strata simi- 



• This is the entrance into the primitive district, whence a mountaiii- 

 road leads to the Mediterranean coast. 



f Similar masses of gravel, but upon a much larger scale, are observetl to 

 form an extensive tract between ihe northern slope of the Samosierra moun- 

 tains, to the north of Madrid, and a formation of compact limestone met with 

 before arriving at Aranda del Duero, on the road from Madrid to Burgos. 

 In both instances the gravel and conglomerate has been formed from ihe de- 

 bris of the primitive rocks in the contiguous chains. 



