British Association . 
689 
1879.] 
dence went the author considers it much more probable that 
the soil is the source of the combined nitrogen. Experi- 
ments show that by the growth of wheat or barley for many 
years in succession on the same land without nitrogenous 
manure, the annual yield of nitrogen in the crop gradually 
diminishes. There was also a diminution in the percentage 
of nitrogen in the soil. In the case of the root crops the 
diminution in the percentage of nitrogen in the soils was 
also greater. With beans there was also a diminution in the 
yield of nitrogen in the crop, but still much more was yielded, 
even at the conclusion, than with either wheat or barley. 
In these cases there was not found a redu&ion of nitrogen 
in the soil. In the case of mixed herbage experiments, very 
much more nitrogen was yielded by the application of potash 
manure, and here there was a great reduction in the per- 
centage of nitrogen in the soil. The percentage of nitrogen 
in the soil was also very largely reduced in the case of clover 
grown for many years in garden soil. Part of this reduction 
might be due to other causes, but the indication was that 
the Leguminosae had derived their nitrogen from the soil. 
Admitting that the sources of the whole of the nitrogen of 
vegetation were not conclusively made out, he nevertheless 
considered that the existing evidence was against the idea of 
the assimilation of free nitrogen by plants, and in favour of 
an opinion that free nitrogen was mainly, if not entirely, 
derived from the soil. 
Section C. 
The President of the Geological Section (C), Professor P. 
Martin Duncan, in his Address, said that of all the geolo- 
gical formations the carboniferous gave the earliest clear 
and definite idea of a land surface on the earth, or rather of 
the existence of many lands. In reflecting upon the history 
of the carboniferous deposits, in relation to the subsequent 
great changes in the physical geography of the earth, the 
idea that geological histories repeated themselves did not 
obtain that importance with which it is credited in relation 
to human events. It was true that there were extensive 
triassic, oolitic, wealden, neocomian, and tertiary lands, 
whose vegetation had been metamorphosed into a kind of 
coal ; but the wonderful depth, and the extraordinary vertical 
repetition of organic and inorganic deposits of the carbon- 
iferous formation, and the remarkable crust movements which 
enabled them to accumulate, were without subsequent 
examples. 
