J. J. Griffith 379 



Influence of Mine Refuse upon the Composition of Soils. 



The analyses of a number of soils are given in Tables V, VI and VII. 

 The mechanical composition is given throughout. The chemical com- 

 position is included only in so far as it presents any points of contrast 

 between affected and unaffected soils. 



Deductions from Table V. 



(a) There is no appreciable alteration in the mechanical composition 

 of the soils. Usually there is only a slight increase in the proportion of 

 fine sand and coarse silt. This change is not likely to have any serious 

 effect upon fertihty. 



(b) With regard to changes in chemical composition it is usually 

 found that the nitrogen content is lowered as a result of contamination. 



(c) The amount of toxic metals, lead and zinc, present is high and 

 much higher than in soils affected by river water. See Tables VI and VII. 



Deductions from Table VI. 



(a) Contamination has brought about a very considerable change 

 in mechanical composition. The coarse grade of particles have been 

 increased to such an extent that the texture of the soils is much too 

 open. See samples Nos. 7, 8 and 27. 



(b) The store of plant food is lowered, both with regard to nitrogen 

 and potash. 



With reference to this point it is to be noted that apart from the 

 alluvial soils of the river valleys the soils of Cardiganshire are very rich 

 in potash and deficient in phosphate and lime, and, generally speaking, 

 are remarkably uniform in their chemical composition. The alluvial 

 soils of the river valleys, on the other hand, are not as rich in potash as 

 the sedentary and glacial soils of the country. As it is mainly the soils 

 in the river valleys that have been affected it is evident that the lowering 

 of the percentage of potash may be one cause of their infertility. 



(c) The toxic metals, lead and zinc, are present in smaller quantities 

 than in leat affected land. Contrast Table V. 



Deductions from Table VII. 



(a) Contamination has not greatly affected the mechanical composi- 

 tion of these soils. In this respect there is a resemblance to leat affected 

 soils; cf. Table V. 



(6) The amount of toxic metals may or may not be high. 



