494 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



In other parts great fissures have been produced, which, being 

 enlarged by the rain-water descending from the slopes, have become 

 wide valleys and precipitous ravines. Such is the condition of the 

 " Tajos del Gaitan " and of several parts of the " Sierra de Abdalagis." 

 In these cases, however, the rocks are regularly worn, without any 

 grooving or different kind of shape, plainly indicating that they 

 have been subject for ages to the same physical action. Thus, a 

 river has shaped its course through the midst of this region, and its 

 powerful denuding effects can be traced at the present day ; but, 

 although we may examine its successive channels from top to bot- 

 tom, we can find nothing that resembles the rapid force exerted upon 

 the Torcal. The " Sierra de la Chimenea" and that of " Las Cabras," 

 which surround this mountain, are conical and quite different in 

 shape : in them we can see the regular effects of the weathering 

 influences on their peculiar calcareous stone ; and I see no reason 

 why everywhere else it should not have been acted upon in the same 

 manner, especially as the stratification in some of these places is as 

 horizontal as in the Torcal. Otherwise we might explain the greater 

 effect then produced, by ascribing it to the coincidence of the course 

 of the water with that of the beds. Moreover the whole chain is 

 equally exposed to any alternations of weather that may have taken 

 place. A. very rapid and jjowerful ageucy must have been required 

 to produce the extraordinary condition of the Torcal. 



The tabulated shape of the top of the Torcal renders it probable 

 that the original summit has been washed away ; so that there a 

 greater force has been exerted than on the slopes. Almost all the 

 basins have profound fissures in their centre; and the mountain is 

 pierced from top to bottom by crevices and vertical caverns. Prof. 

 Ansted has observed that the volcanic rocks which have lifted the 

 Sierra Nevada and other chains of Andalusia are rarely if ever to be 

 seen at the sui-face. Now it is remarkable that the foot of the 

 Torcal is one of the few places where these rocks can be found ; for 

 on both sides a peculiar sort of greenstone is seen in some abundance. 

 I am therefore inclined to believe that this mountain has been the 

 centre of the upheaval occasioned by the above-mentioned rocks, not 

 only because it seems to be the point of connexion between the 

 adjoining Sierras, but also on account of its being situated in the 

 centre of the region and its strata being so horizontal, whilst those 

 of the extremities, as, for example, at the Tajos del Gaitan, have 

 been thrown into all sorts of inclinations, even becoming vertical at 

 the place called " El Cherro," at the extreme end of the chain. 



