294 VELD-CURNING EXPERIMENTS AT GROENKLOOF, PRETORIA. 



A- Stones near surface. Soil yellowish, either very little change or may 

 change to a yellowish brown after the first two inches. 



B. Soil yellowish for 8 inches and then darker yellow, stony as sample A. 



C. Soil reddish, not stony. 



Mechanical analysis of these three samples yielded the results tabulated 

 below : — 



The percentage composition of the samples as collected in the field, 

 after drying, was as follows : — 



Stones above Coarse gravel. Soil below 

 .3 mm. 3-2 mm. 2 mm. 



A 37-85 3.II 5904 



B 26.84 5.57 57-59 



C nil. 0.26 99.74 



The above 2 mm. produci, on further differentiation, was found to 

 be composed as follows : — 



Fine gravel Coarse sand Medium sand Fine sand 



2-1 mm. 1-.5 mm. .5-.25 mm. .25-. i mm. 



A 1016 20.20 29.31 17-85 



B 9.67 20.42 27.12 14-77 



C 12.74 23.70 29 20 17.33 



Very fine Silt Fine silt Clay 



sand .1-.05 mm o5.-.or mm. .oi--oo5 mm. below .005 mm- 



A- 10.16 20.20 29.31 17.85 



B 9.67 2042 27.12 14.77 



C 12.74 23.70 29.20 17.33 



It will be seen that after sifting away the pebbles and coarse gravel 

 the mechanical make-up of tlie residual soils is very similar. This becomes 

 more oI)vious on stripping of their decimals the percentages in the last 

 table, thus : — 



Fine Coarse Medium Fine Very fine Silt Fine 

 gravel sand. sand. sand. sand. silt. Clay. 



A 5 3 6 8 10 20 29 18 



B- 8 4 8 8 10 20 27 15 



C 2 2 6 7 13 24 29 17 



Grouping all the sand grades togetlier. and likewise the silt grades, 

 the following figures are arrived at : — 



Fine gravel. Sand- Silt. Clay. 



A 5 3S 49 18 



B 8 30 47 15 



C 2 28 53 17 



C. is therefore very sliglitly finer-grained than A- or B., but I would 

 class all three as fine-grained loam soils, almost approaching to silt-loams, 

 but all three clearly belong to the same series. The high percentages of 

 silt render such soils as C. valuable for wheat cultivation (leaving the 

 chemical composition of the soil out of consideration for the moment). 

 In the United States, the Norfolk silt loam is regarded as one of the 

 most valuable soils of the Atlantic coastal plain for general farm crops, and 

 is best adapted for wheat, maize and grass ; its average mechanical com- 

 position is : — 



Fine gravel. Sand. Silt. Clay. 

 I .31 54 12 



Another American soil that is physically very similar to A. and B. 

 is the stony loam of the Miami series, which contains from 20 to 60 per 

 cent- of rounded and angular stones varying from 1-8 inches in diameter. 

 This soil, too, is very productive, producing, amongst others, good crops 



