194 THE CHEMISTRY OF GARDEN CROPS 



become loamy through accumulation of humus. Between the oldest 

 limestone and the latest chalk there are many intermediate kinds of 

 calcareous soils, and they are mostly good, owing to their richness in 

 phosphates, the products of the marine organisms of which these 

 rocks in great part, and in some cases wholly, consist. For the 

 growth of cereals these calcareous soils need a certain proportion of 

 silica, and where they have this we see some of the finest crops of 

 Wheat, Trifolium, and Peas and Beans in all these islands. If we 

 could mix some of our obdurate clays with our barren limestones, the 

 two comparatively worthless staples would probably prove remarkably 

 fertile. Although this is impossible, a consideration of the chemistry 

 of the imaginary mixture may be useful, more especially to the 

 gardener, who can in a small way accomplish many things that are 

 out of the region of practice on a great scale. Sandy soils are 

 characterised by excess of silica, and deficiency of alumina and 

 phosphates. But here the mechanical texture is as serious a matter 

 as it is in the case of clay. The sand is too loose as the clay is too 

 pasty, and it may be that we have to hold the estate as it were in our 

 hands to prevent it from being blown away. It is especially worthy 

 of observation, however, that sandy soils are the most readily amen- 

 able of any to the operation of tillage ; and if we cannot take much 

 out of them, we can put any amount into them, and must always 

 calculate nicely where the process of enrichment is to stop. It is not 

 less worthy of observation that sandy soils can be rendered capable 

 of producing almost every kind of crop, save cereals and pulse, and 

 even these can be secured where there is some basis of peat or loam 

 or clay with the sand. The parks and gardens of Paris, Versailles, 

 Haarlem, and Berlin are on deep sands, that are blown away when 

 left exposed for any length of time with no crop upon them to prevent 

 direct contact of the wind with the soil ; and not only do we see the 

 finest of Potatoes and the most nutritious of herbage produced on 

 these soils, but good Cauliflowers, Peas, Beans, Onions, fruits, and big 

 trees full of sound timber. It would be inaccurate to say that any soil 

 is beyond improvement, for the plough has found its way to the foot 

 of Stonehenge, where only a hundred years ago cultivation was 

 declared impossible, and on the granite of Dartmoor we. may now 

 see a fine grass sward where not long since the only vegetation com- 

 prised lichens and mosses. The farming and gardening at Prince 

 Town owe their success in great part to the judicious use of sewage, 

 and thus illustrate the immense importance of the subject before us. 

 Garden soils usually consist of loam of some kind, the consequence 



