The causes of this variation in the ash-content of peat, deserve a moment's notice. The plants that produce peat contain considerable proportions of lime, magnesia, alkalies, sulphuric acid, chlorine and phosphoric acid, as seen from the following analysis by Websky. COMPOSITION OF THE ASH OF SPHAGNUM. Potash. 17.2 Soda. 8.3 Lime. 11.8 Magnesia. 6.7 Sulphuric acid. 6.5 Chlorine. 6.2 Phosphoric acid. 6.7 _Per cent._ of ash, 2.5. The mineral matters of the sphagnum do not all become ingredients of the peat; but, as rapidly as the moss decays below, its soluble matters are to a great degree absorbed by the vegetation, which is still living and growing above. Again, when a stream flows through a peat-bed, soluble matters are carried away by the water, which is often dark-brown from the substances dissolved in it. Finally the soil of the adjacent land is washed or blown upon the swamp, in greater or less quantities. III.--_The decomposition of peat in the soil offers some peculiarities_ that are worthy of notice in this place. Peat is more gradual and regular in decay than the vegetable matters of stable dung, or than that furnished by turning under sod or green crops. It is thus a more steady and lasting benefit, especially in light soils, out of which ordinary vegetable manures disappear too rapidly. The decay of peat appears to proceed through a regular series of steps. In the soil, especially in contact with soluble alkaline bodies, as ammonia and lime, there is a progressive conversion of the _insoluble_ or _less soluble_ into _soluble_ compounds. Thus the inert matters that resist the immediate solvent power of alkalies, absorb oxygen from the air, and form the humic or ulmic acids soluble in alkalies; the humic acids undergo conversion into crenic acid, and this body, by oxidation, passes into apocrenic acid. The two latter are soluble in water, and, in the porous soil, they are rapidly brought to the end-results of decay, viz.: water, carbonic acid, ammonia and free nitrogen. Great differences must be observed, however, in the rapidity with which these changes take place. Doubtless they go on most slowly in case of the fibrous compact peats, and perhaps some of the lighter and more porous samples of swamp muck, would decay nearly as fast as rotted stable dung. It might appear from the above statement, that the effect of exposing peat to the air, as is done when it is incorporated with the soil, would be to increase relatively the amount of soluble organic matters; but the truth is, that they are often actually diminished. In fact, the oxidation and consequent removal of these soluble matters (crenic and apocrenic acids,) is likely to proceed more rapidly than they can be produced from the less soluble humic acid of the peat. IV.--_Comparison of Peat with Stable Manure._