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



139 



accumulations of combined nitrogen, they possess further and greater 

 value as representing the materials from which large areas of our 

 soils are derived. 



With regard to the amounts of nitrogen in the various deposits (see 

 Table VII), the results show less variation than might be expected, 

 the percentages being, in nine cases out of eleven, between 0*032 

 and 0*053. The limits in the case of carbon are, however, much 

 wider apart — 0*299 to 1*299 ; and it is evident that the organic 

 matter as a whole must vary greatly in its character. In every 

 case the organic matter will include a variety of substances ; and it 

 is conceivable that the nitrogenous matter, in the London Clay for 

 instance, may be very similar to that of the Rothamsted subsoil, 

 the excess of carbon in the London Clay being due to the presence 

 of some non-nitrogenous substances. The relatively high amount 

 of nitrogen in the Kimmeridge Shale is somewhat unexpected, and 

 may in part be connected with the presumably animal origin of the 

 deposit. In contrast to this, we find in the Purbeck Clay (No. 5) 

 more than 40 times as much carbon as nitrogen. 



Table VII. — Carbon and Nitrogen in Clays and Marls. 



Calcium- 

 carbonate. 



Organic 

 carbon. 



Per cent. 



1. Lower Lias 15*8 



2. Oxford Clay '■ 21*4 



3. Kimmeridge Shale 



4. Purbeck 



5. Do 



Subwealden 



6. Wealden 



7. Do 



8. Gault 



9. Chalk-Marl 



10. London Clay 



52*2 



82-1 

 73*4 



Per cent. 

 0-847 

 0-786 

 0-386 

 0470 

 1-299 



[Oxford I Clay] 



5-8 



30-6 

 35-4 



7-9 



1-229 

 0534 

 0-613 

 0-299 

 0391 



Total 



Carbon 

 to 1 of 



nitrogen, carbon 



Per cent. 

 0-051 

 0-053 

 0-036 

 0021 

 0-032 

 0-044 



16-6 

 14-8 

 10-7 

 22-4 

 40-6 



Nitrogen 

 to 100 of 



0-069 



17*8 



0033 



160 



0-036 



17*0 



0033 



8*8 



0-041 



95 



60 

 67 

 9-3 

 44 

 2-6 



5-6 



6-2 



5-8 



110 



10*5 



Speculation as to the precise nature of these various forms of 

 organic matter, and the causes of the variations in their composition, 

 is, however, premature. The important question is whether, in the 

 case of these older deposits, the organic matter which is evidently, 

 sometimes at any rate, of a bituminous nature, contains any humus 

 at all — the term humus including not only the substances soluble 

 in weak alkali, but also the insoluble residues of decaying vegetable 

 matter. The distinction is of considerable importance in agriculture,, 



l2 



