66 Colonel Silvertop on the Lactistrine Basins of' 



Elvira, near Granada, is seen within this area : with this ex- 

 ception, the whole of its superficies is occupied by conglomerates, 

 marl, gypsum, and other tertiary beds ; the conglomerates pre- 

 dominating to the north and east of Granada, and forming a 

 high tract of waving hilly ground between this city and the 

 Sierra Nevada ; the latter prevailing to its south, or from the 

 left bank of the river Genii to the ridge which confines the 

 basin in the latter direction. The upper stratum of the valley 

 of the Genii, which occupies the lowest relative tract in this 

 basin, is generally composed, near Granada, of a disintegrated 

 conglomerate, an argillaceous marly deposit, with innumerable 

 rounded fragments of the neighbouring primary and transition 

 rocks; but lower down it often consists of a sandy loam. The 

 rising ground from this valley in the direction of a village called 

 Cogollos, situated at the base of the ridge which bounds the 

 basin towards the north, exhibits a high, broken, irregular tract, 

 consisting of a calcareous marly deposit, with some beds of 

 marly sandstone two or three inches thick, and containing, as I 

 was informed, some beds of lignite *. Near Alfacar, another vil- 

 lage upon this slope, there is an extensive formation of calca- 

 reous tufa, which is quarried, and has furnished the material 

 with which several of the churches in Granada have been built -|-i 

 it passes in some places into beautiful alabaster, which receives the 

 most brilliant polish, and is worked into slabs, vases, and other 

 ornamental figures. 



There is one circumstance perhaps worthy of being noticed, 

 connected with the conglomerate hills between Granada and the 

 Sierra Nevada. A stream called El Uaro, taking its rise near 

 the village of Huetor de Santillana, and entering the Genii at 

 Granada, winds its intervening course between high hills of this 

 deposit. After heavy rains have increased the volume and ra- 

 pidity of its waters, and transported to its bed the loose mate- 

 rials of the adjoining hills, it is not unusual to find pai'ticles of 

 gold disseminated in the sand and mud deposited after the tor- 



• I had no opportunity to examine this tract, but presume it to be tertiarj. 



•j- Extensive deposits of calcareous tufa are observable in many parts of the 

 south of Spain, generally along the bases of limestone ridges. Natural exca- 

 vations in these constitute caverns, often of singular beauty ; that called 

 St Michael's at Gibraltar, is well known. 



