252 GEOLOGICAL SURVEY 
If the sulphate of amonia be bronght in contact with carbonate of lime, decomposition again, in 
the reverse order, takes place, provided that there be no excess of water, and that the two be not 
altogether dry, but having that degree of humidity which is found in well drained soils, and carbo- 
nate of amonia and sulphate of lime are again formed. Now it must be recollected that it is the 
carbonate of amonia alone that is useful to plants, although it is laid up, as it were, for use, in the 
form of sulphates. So muriate, phosphate, and oxalate of amonia, produce no useful efiect; but 
when brought in contact with carbonate of lime, under the circumstances of humidity amd porosity 
existing in well drained, cultivated land, they are converted into carbonate of amonia. This shows 
the value of carbonate of lime in the soil, even where it may be found in another form. Does it 
not explain the more energetic action of gypsum on marled land? Does it not also indicate marl- 
ing as the proper remedy for the excess of muriate of soda and other salts, in recently reclaimed 
salt marsh? ’ 
The noxious salts that often exist in soils saturated with stagnant water, are removed by drainage, 
and the soil in effect deepened. Nothing is more common than to see a crop grow luxuriantly for 
some time, in its carly stages, and after that to fail totally. Before the mtroduction of systematic 
draining, in Scotland, this used to take place over considerable districts of country. The cause 
was this; a soil may be drained to a depth of two or three inches, and yet may be wet below that. 
This depth of soil may be sufficient for plants at first, but when they grow larger, and extend their 
roots deeper, the soil drained is not sufficient to furnish the conditions required for healthy growth, 
and the effect above stated is the result. 
Numerous other examples might be given, to show the favorable conditions induced in the soil 
by drainage, but these must suffice. 
Vloughing, in some of its effects, resembles draining, and ranks high among the mechanical 
means of improving the soil. Sub-soil ploughing is, indeed, a mode of draining that, under certain 
circumstances, is quite efficient. It has an obvious advantage over deep ploughing, where it is not 
safe to turn. up the sub-soil, at the same time that it is necessary it should be broken and rendered 
permeable. 
Attention to the nature of the sub-soil will prevent the mistakes committed in deep ploughing, 
where it is turned up. When the sub-soil is good it may be brought to the surface, but always cau- 
tiously, especially where the soil is not a deep and porous loam; and there is the more caution 
required where a pretty good soil has been made, by good tillage, cn a poor subsoil. Yet deep 
ploughing is the only practicable means of increasing the depth of the soil, a condition of great 
importance. A deep, porous soil is less liable to the waste from washing than a thin one, because 
the rain sinks into it, and is retarded in its downward progress. Drainage and gradual deepen- 
ing of the arable soil should always go hand in hand. 
SoILs oF THE STATE. 
The classification of the soils of the State, which is here proposed, is one founded on their geo- 
logical relations, or, in other words, upon the rocks from which they are derived. The name will 
always convey some general idea of the character of the soils, at least in the upper part of the 
State. The soils of the Tertiary formation are not so easily classified, as they are derived from 
