138 



DR. N. a. J. MILLER ON THE AMOUNTS OF [May I903, 



An example of a soil may now be given, in which carbon was 

 retained in unusually large amounts. The soil, which was obtained 

 in 1882, was unbroken prairie-land near Selkirk (Manitoba). Both 

 the organic carbon and the total nitrogen in the surface-soil, which 

 is nearly black, are very high ; but the soluble nitrogen, although 

 present in considerable quantity, is lower in relation to the total 

 nitrogen than is the case in Eothamsted soils. 



Table VI. — Organic Carbon and Nitrogen in Manitoba Prairie-Soil. 



Depths 



of 



12 inches. 



Organic 

 carbon. 



Total 

 nitrogen. 



Carbon 



tolof 



nitrogen. 



Nitrogen, 

 to 100 of , 

 carbon. 



Soluble 

 humus. 



Nitrogen 



in soluble 



humus. 



Soluble 

 nitrogen 

 in soil. 





Per cent. 



Per cent. 





Per cent. 



Per cent. 



Per cent. 



1st 



7-58 



0-618 



12-3 



8-2 



5-93 



4-08 



02423 



2nd 



3-68 



0-264 



13-9 



7-2 



— 



— 



— 



3rd 



1-53 



0076 



20-0 



5-0 





— 



— 



4th 



1-09 



0-042 



26-0 



3-9 







— 



— 



The sudden fall in the percentage of nitrogen in the subsoil 

 is very striking. At a depth of 4 feet the amount of nitrogen 

 is very nearly the same as in the Rothamsted subsoil. The per- 

 centage of carbon is, however, unusually high, and the organic 

 matter as a whole very different in composition from that present 

 in our clay-subsoil. 



Composition of the Deep Clays and Marls. 



The samples of the various deposits were obtained, through the 

 kindness of Sir Archibald Geikie, from the Geological Survey. The 

 following is a list arranged in chronological order : — 



1. Lower Lias. Mickleton Boring (Gloucestershire). 



2. Oxford Clay. Brabourne Boring, at 1370 feet. 



3. Kiruineridge Shale. Subwealden Boring, Netherfield (Sussex). 



4. Purbeck. Penshurst Boring, at 1074 feet. 



5. Do. do. do. at 1015 feet. 



6. Wealden. Brady Shaft, Dover, 472-478 feet. 



7. Do. Mottled clay. Brabourne Boring, at 591-611 feet. 



8. Gault. Meux's Brewery, Tottenham Court Road. 



9. Chalk Marl. Meux's Brewery. 



0. London Clay, from Electric Pvail way-Tunnel, Piccadilly Circus. 



In addition to the above, reference will be made to a sample of 

 Oxford Clay, obtained in 1876 from the Subwealden Exploration 

 Boring, at a depth of between 500 and 600 feet. 



Apart from the interest due to the great depths at which the 

 samples were obtained, and the evidence that they afford of enormous 



