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this class cannot be placed to the sun's credit, as 

 some may be due to heat that has its source beneath 

 the surface of the earth, while many are due to the 

 movements in the earth's crust. 



If the sun acts alone or only in conjunction with 

 wind, it is a destroyer; but when it is joined with cold 

 and rain, the effects are modified, as all combined, cause 

 vegetation which eventually clothes the surface of the 

 ground with a protecting envelope. Thus it is evident 

 that the sun ought to accomplish its maximum 

 amount of denudation in tropical regions ; yet the 

 amount of work done in the temperate zone must be 

 considerable, if we may judge from what can be ob- 

 served in Ireland, as the part the sun has taken in form- 

 ing its present features is conspicuous. All the hills in 

 that island, with very few exceptions, have much 

 longer slopes towards the south than towards the 

 north. These may have gradual slopes southward, 

 while northward the cliffs are more or less preci- 

 pitous; and with scarcely an exception, all the streams 

 in a mountain group that flow southward have their 

 source and watershed close to the summit of the 

 escarpment that bounds the high lands on the 

 north, so that respectively in all mountain groups 

 the streams that flow southward are much more con- 

 siderable than th3 streams that flow northward. This 

 is apparently due to the rays of the sun acting as a 

 denudant on those parts of the land that are most 



