OPERATION OP DEEPENING SOIL. 169 



(which were before concealed in some measure by so much enrich- 

 ing matter) become evident. Sorrel and broom-grass cover the 

 land, and if allowed to stand, pines will then take complete pos- 

 session, because the poverty of the soil leaves them no rival to 

 contend with. 



Marling deepens cultivated sandy soils, even lower than the 

 plough may have penetrated. This was an unexpected result, and 

 when first observed seemed scarcely credible. But this effect also 

 is a consequence of the power of calcareous earth to fix manures. 

 As stated in the foregoing paragraph, the soluble and finely divided 

 particles of rotted vegetable matters are carried by the rains below 

 the soil ; but as there is no calcareous earth there to fix them, they 

 must again rise in a gaseous form, after their last decomposition, 

 unless previously taken up by growing plants ; [or descending still 

 lower in the sub-soil, dissolved in rain-water, may go off into the 

 sources of springs, and so be lost to the land.] But after the soil 

 is marled, calcareous as well as putrescent matter is carried down 

 by the rains as far as the soil is open enough for it to pass. This 

 will always be as deep as the ploughing has been, and somewhat 

 deeper in loose earth; and the chemical union formed between 

 these different substances serves to fix both, and tJms increases the 

 depth of the soil. This effect is very different from the deepening 

 of a soil by letting the plough run into the barren sub-soil. If, 

 by this mechanical process, a soil of only three inches is increased 

 to six, as much as it gains in depth, it loses in richness. But when 

 a marled soil is deepened gradually, its dark colour and apparent 

 richness are increased, as well as its depth. Formerly, single-horse 

 ploughs were used to break all my acid soils, and even these would 

 often turn up sub-soil. The average depth of soil on old land did 

 not exceed three inches, nor two on the newly cleared. Even be- 

 fore marling was commenced, my ploughing had generally sunk 

 into the sub-soil and since 1825, most of this originally thin soil 

 has required three mules, or two good horses to a plough, to break 

 the necessary depth. The soil is now from six to eight inches 

 deep generally, from the joint operation of marling and deepening 

 the ploughing a little in the beginning of every course of crops ; 

 [and to that depth, or very nearly, the land is now ploughed when- 

 ever preparing for corn, or for wheat on clover. The summer 

 ploughing of clover land requires four mules to a plough. 



Since marling was begun, the deepening of the soil has much 

 more generally preceded than followed the deepening of the plough- 

 ing. How destructive to the power of soil this present depth of 

 ploughing would have been, without marling, may be inferred from 

 the continued decrease of the crop, through four successive courses 

 of a very mild rotation, on the spot kept without marl in experi- 

 ment 10. Yet the depth of ploughing there did not exceed six 

 15 



