THE GLACIAL PERIOD. 



217 



and earth, the whole 

 forming a rock-mass 

 as solid as the lime- 

 stone of Gibraltar 

 itself. It varies in 

 thickness from a few 

 feet up to 30 or 40 

 yards, and it may be 

 thicker than that 

 where it enters the 

 sea, for the base of 

 shale and limestone 

 on which it rests 

 is not there visible. 

 It covers wide areas 

 of the low grounds, 

 especially in the dis- 

 trict of Buena Vista 

 and Eosia, and in 

 the neighbourhood 

 of the South Bar- 

 racks, attaining its 

 greatest thickness 

 towards the sea, and 

 thinning off as it ap- 

 proaches the steeper 

 slopes of the Eock. 

 All round the Eock 

 similar masses of 

 breccia occur. There 

 can be no possible 

 doubt that these 

 breccias have been 



derived from the Eock itself; they consist exclusively of 

 angular fragments of limestone, not a single stone foreign to 

 the place being visible. It is also equally certain that what- 



