Whether exposed to the air or not, the organic matter suffers internal decomposition, and portions of its elements assume the gaseous or liquid form. We have seen that ripe peat is 10 to 12 _per cent._ richer in carbon and equally poorer in oxygen, than the vegetable matters from which it originates. Organic matters, in passing into peat, lose carbon and nitrogen; but they lose oxygen more rapidly than the other two elements, and hence the latter become relatively more abundant. The loss of hydrogen is such that its proportion to the other elements is but little altered. The bodies that separate from the decomposing vegetable matter are carbonic acid gas, carburetted hydrogen (marsh gas), nitrogen gas, and water. Carbonic acid is the most abundant gaseous product of the peaty decomposition. Since it contains nearly 73 _per cent._ of oxygen and but 27 _per cent._ of carbon, it is obvious that by its escape the proportion of carbon in the residual mass is increased. In the formation of water from the decaying matters, 1 part of hydrogen carries off 8 parts of oxygen, and this change increases the proportion of carbon and of hydrogen. Marsh gas consists of one part of hydrogen to three of carbon, but it is evolved in comparatively small quantity, and hence has no effect in diminishing the _per cent._ of carbon. The gas that bubbles up through the water of a peat-bog, especially if the decomposing matters at the bottom be stirred, consists largely of marsh gas and nitrogen, often with but a small proportion of carbonic acid. Thus Websky found in gas from a peat-bed Carbonic acid 2.97 Marsh gas 43.36 Nitrogen 53.67 ------ 100.00 Carbonic acid, however, dissolves to a considerable extent in water, and is furthermore absorbed by the living vegetation, which is not true of marsh gas and nitrogen; hence the latter escape while the former does not. Nitrogen escapes in the uncombined state, as it always (or usually) does in the decay of vegetable and animal matters that contain it. Its loss is, in general, slower than that of the other elements, and it sometimes accumulates in the peat in considerable quantity. A small portion of nitrogen unites with hydrogen, forming ammonia, which remains combined with the humic and other acids. PART II. ON THE AGRICULTURAL USES OF PEAT AND SWAMP MUCK. After the foregoing account of the composition of peat, we may proceed to notice: 1.--_The characters that adapt it for agricultural uses._ These characters are conveniently discussed under two heads, viz.: Those which render it useful in improving the texture and physical characters of the soil, and indirectly contribute to the nourishment of crops,--characters which constitute it an _amendment_ to the soil (_A_); and Those which make it a direct _fertilizer_ (_B_). A.--Considered as an amendment, the value of peat depends upon