of Baza and Alhama. 85 



beautiful impression or mould of a large planorbis: now, as 

 this univalve is not met with in the compact limestone, but first 

 makes its appearance in the coarse marly limestone, almost en- 

 tirely composed of comminuted shells of this genus, which over- 

 lies theTormer near Alhama, and is the superior rock seen in 

 that basin, this circumstance leads to .the conclusion, that the 

 magnesite of Ballejas, like the superior marly limestone near 

 Alhama, is of lacustrine origin, and amongst the most modern 

 rocks in Spain, — as a similar one has already been shewn to be 

 so in France, by Messrs Brongniart, Marcel de Serres, and 

 other writers. . ^ 



4. The last instance of a lacustrine formation which I have 



t . . . •• 



had an opportunity of meeting with in Spain, is presented over 

 an extensive tract in the neighbourhood of Teruel, a town upon 

 the frontier of Arragon, towards the province of Valencia, and 

 upon the road from the city of Valencia to Zaragoza. The an- 

 nexed rough sketch may give a general idea of this lacustrine 

 deposite, and of the older rocks which bound it towards the east 

 and west. . . ^ . r 



Lacustrine Basin of Teruel^ Province of Arragon. 



yr ■•■./■ 



-^ ^ CuDeep'Bttvlnc'^^ ■ ZenaiL 



l.^ I, ^-^ \ 



o a a is a coarse, in places vesicular limestone full of lymneje and planorbes. 



bh hS&Q. thick bed of reddish gravelly marl, occasionally containing gypsum. 



3. Secondary nummulite limestone. 



2. Red sandstone, — old ? 



1. Greywackd ridge. ' 



Z. A dark blue semi-crystalline limestone. 



The superior fresh-water limestone a a a, would appear to 

 have originally prevailed, as represented in the sketch, over the 

 whole width of the basin from y X.o y^ a distance of about 16 

 miles ; but causes, whose violence or prolonged duration is ma- 

 nifest in the valleys of denudation and deep ravines which ac- 

 tually intersect this area, have swept it away over .the. greater 

 portion of the basin. Where it remains sufficiently; entire, it 

 forms patchs of table-land, and the slopes. from these' to adjoin- 

 ing fissures exhibit an irregular talus of the subjacent marly de- 



