SOUTH-WEST IRELAND. 179 



account, however, of the jointed and faulted condition 

 of the rocks, it often can advance more rapidly in 

 certain places than elsewhere ; for if it meets with a 

 dyke of loose fault-rock, or a tract of strata broken by 

 joints or faults, it works more quickly along these, 

 thereby at such places excavating a passage across 

 the strata, whether hard or soft. After crossing hard 

 beds, however, besides advancing, it will also work 

 sideways, eating out longitudinal hollows along the 

 soft strata. Work of this kind can be studied in 

 Cork Harbour, the sea having cut narrow north-and- 

 south guts through two bands of grits of Old Red 

 Sandstone age, while in the intervening Carboni- 

 ferous limestones and shales it is excavating E. and 

 W. bays. It might be argued that none of this work 

 should be claimed as due to marine denudation, be- 

 cause that when the land was relatively higher, a river 

 may have flowed through Cork Harbour, while tribu- 

 tary streams, with the auxiliary meteoric abrasion, was 

 excavating out valleys in the limestone and shale, 

 which now are submerged, and form the lateral bays. 

 Such may have been the case in other places, but here 

 we know that the land is relatively sinking, and has 

 been doing so for centuries, while at the present day 

 the sea is yearly denuding the coast-line more and 

 more. Consequently it is only leaving fact to go to 

 supposition to state that a force which is not now 

 acting probably did work which we know by ocular 



