Vol. 59.] NITROGEN AND CARBON IN CLAYS AND MARLS. 141 



regard, either from the paper or from the discussion. The amounts 

 of carbon and nitrogen in the subsoil were, however, of consider- 

 able geological interest. He pointed out that the percentage of 

 nitrogen was stated to be higher in the Kimmeridge Clay than in 

 the Purbeck Clays; and, as a rule, Kimmeridge-Clay soils were 

 fertile. As to the manurial values of subsoils, it was advisable 

 to consult experience rather than theory. Most blue clays, when 

 added to a soil, diminished its value ; it was far better to add a red 

 (or thoroughly oxidized) subsoil, and the best that he knew of was 

 the red Permian ' marl' of Devon. 



