SOUTH-WEST IRELAND. 199 



bases, till eventually slopes are formed ; on this ac- 

 count valleys usually move away from their faults, the 

 rocks on the down-throw side, which usually rise to 

 the fault, being more easily denuded than those on 

 the other side. Wind, however, as previously pointed 

 out (page 80), may act very similarly to a stream of 

 water in keeping a cliff perpendicular. Joints or 

 other shrinkage fissures will also affect the weather- 

 ing of a cliff, according as they are nearly parallel 

 or perpendicular to the line of cliff, as previously 

 illustrated when speaking of the marl cliffs in south- 

 east Ireland (page 51). 



In the Weald there would appear to have been 

 at one time more or less continuous cliffs to the 

 north, east, and south of the clay country, probably at 

 the commencement of the Forest period ; these, how- 

 ever, seem to have been denuded back since then, and 

 modified by meteoric abrasion, which first changed 

 the cliffs into slopes, and afterward gradually denuded 

 the latter backwards ; so that now the escarpments 

 may be far removed from the original sites of the 

 cliffs, and during all this time the transverse valleys 

 across the Downs must have been somewhat simi- 

 larly acted on. If the sea had formed cliffs to the 

 Weald valley, it would necessarily have worn back 

 both the chalk and the harder underlying strata ; 

 such, however, would not be the case with meteoric 

 abrasion, as this agent would have greater effect 



