GORGES AND RAVINES. 165 



aid of much denudation or any convulsion of Nature. 

 It has been already shown that when two or more 

 fissures meet or cross each other, a greater or less 

 vacancy is formed (fig. 5, PI. I.) ; and from an examina- 

 tion of the geological map accompanying Blanford's 

 description, we learn that various valleys radiate from 

 this lake-basin, and if valleys, probably also breaks. 

 Here, therefore, a greater or less vacancy ought to 

 have been formed, and after it had been modified 

 by meteoric abrasion, it would be represented by the 

 present lake-basin. Blanford has suggested that 

 this lake-basin " must be of very small geological 

 antiquity, or it would have filled up long since." This, 

 however, would be quite unnecessary if the valleys 

 and basin are principally due to the shrinkage of 

 the rock ; as then the materials to be denuded would 

 be of but small amount, and any that did go down 

 may be yearly carried away by a subterranean passage 

 similar to that which Blanford supposes to exist ; l as 

 other lakes with similar outlets have been found to 

 be capable of discharging the detritus brought into 

 them by streams. This is particularly evident, both 

 in the Counties Clare and Galway ; as many of the 

 lake-basins, there, would long since have been filled 

 up by the solid matter borne into them, were it not 



1 Mr Blanford points out that circumstances over which he had no 

 control prevented him giving the time he would have wished to the 

 examination of the Abyssinian lake-basins, but to this lake-basin he paid 

 particular attention. 



