1900] Shutt— Soils. 43 



stituents : mineral or inorg-anic, derived from the disintegration 

 ot the original rock surface of the earth, and organic, resulting 

 from the decay of past generations of plants, and grouped under 

 the general term humus. Besides these, air and water are present, 

 making the soil a suitable and comfortable medium for the growth 

 of plants, and playing an important part in the preparation of their 

 food. And, lastly, as we have learned in recent years, there are in 

 every fertile soil myriads of micro-organisms, working, under con- 

 ditions that afford them warmth and moisture and air, in the con- 

 vertion of inert or locked-up plant nourishment of the soil into 

 substances and compounds more or less immediately available for 

 crops. The transformation of the useless nitrog-en of humus, first 

 into nitrites and finally into nitrates, is an important example ot 

 the valuable work done for agriculture by these microscopic 

 plants. 



We must not now stay to consider in detail the origin of 

 soils nor the various natural ag-encies and forces that have been 

 and are now at work in their formation. The whole subject is 

 one of peculiar interest and magnitude, and merits a much more 

 careful and systematic treatment than would be possible in this 

 lecture. I can do little more than mention the fact that agricul- 

 turally, as well as geologically, the name of soils is legion. There 

 are clay -^oils and sandy soils, so called from the predominance of 

 clay and sand respectively, and soils rich in humus, and a host of 

 intermediate soils known as loams. Save in the case of trans- 

 ported soils, such as the deltaic soils formed at the mouth of 

 rivers, their mineralogical composition will accord with that of 

 the underlying rock. But whatever the nature of soils, their chief 

 agricultural function always remains the same, viz., to furnish 

 certain mineral substances, among which potash, phosphoric acid 

 and lime are the most prominent ; to offer, in combined forms, 

 nitrogen, a further essential for plant life ; to hold moisture and 

 air necessary for the growth of plants, and to form a firm, com- 

 fortable and warrn support for their growth. 



Before proceeding to speak of the amounts of plant food in 

 soils, it is desirable that I should call your attention to the im- 

 portance of humus as a soil constituent, since the method of 

 employing clover at a fertilizer, which I am to bring before you 



