HORTUS GRAMINEUS WOBUliNKNSIS. 117 



soil, and consequently to describe the same without any risk of 

 being misunderstood, which before this was absolutely unavoid- 

 able. 



All soils consist of sand of various degrees of fineness, and 

 impalpable earthy matter ; when, therefore, the exact proportions 

 in which these are combined in a soil are known, with their ge- 

 neral properties, it shews directly to which class of soil it belongs ; 

 whether to the loamy, clayey, calcareous, sandy, peaty, &c. 



Sir Humphry Davy, in his " Elements of Agricultural Chemistry," 

 states the proportions of sand and impalpable earthy matter, to 

 which the terms usually adopted should be limited. " The term 

 sandy should never be applied to any soil that does not at least 

 contain seven-eighths of sand ; sandy soils that effervesce with 

 acids, should be distinguished by the name of calcareous sandy 

 soil, to distinguish them from those that are siliceous. The term 

 clayey should not be applied to any land that contains less than 

 one-sixth of impalpable earthy matter, not considerably effer- 

 vescing with acids ; the word loam should be limited to soils 

 containing at least one-third of impalpable earthy matter. A soil 

 to be considered as peaty ought to contain at least one-half of 

 vegetable matter." These may be considered as the generic cha- 

 racters of soils, and determined by a very simple process that of 

 washing the impalpable earthy matter of the soil from the sandy 

 portion, and by drying and ascertaining their respective weights, 

 when the application of an acid shews whether it belongs to the 

 calcareous or siliceous kinds of soil. 



The results of all my observations in these experiments on 

 grasses, and likewise in the cultivation of a large collection of 

 plants on various kinds of soil, tend to confirm the opinion, that 

 the fitness or unfitness of particular soils for particular plants, 

 depends, in a general sense, on the due proportions of sand and 

 impalpable earthy matter of which they consist. If writers, 

 therefore, on the comparative produce of plants, whether of the 

 farm or the garden, would only thus far describe the nature of the 

 soils employed in their experiments, the benefit of it would be felt 

 and duly appreciated by every practical person ; but more so, by 

 those who wish to repeat such experiments. But misconception 

 with respect to the nature of soils employed in experiments must 

 be effectually prevented by ascertaining the number and propor- 

 tion of the constituent parts, because the smallest difference in 

 the natural qualities of soils is thereby detected. It would surely 



