666 Scientific Proceedings, Royal Dublin Society. 



Opportunity for this research was provided by a maintenance grant from 

 the Department of Scientific and Industrial Eesearch. 



The writer wishes to express his indebtedness to Professor H. H. Dixon 

 and Major W. E. G. Atkins, at whose instigation the work was undertaken ; 

 and to Capt. N. G. Ball for his assistance in the soil analysis. 



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