To the vegetation inhabiting the swamps during this period, man owes a debt perhaps as great as to our modern food plants, for it is upon this, and some later plant remains, that we rely for coal. This period has been well called the Carboniferous, for its chief claim to attention, outside the realms of botanical research, was the deposition of those great collections of plant remains, which, as coal, contain as high as 90 per cent of carbon and furnish the fuel of the world. This is scarcely the place or time to go into the composition of different kinds of coal, but some mention of the conditions under which these ancient swampy forests were transformed into that valuable substance may well conclude the account of a vegetation period the history of which has in large part been found written in the very strata from which coal itself is derived. In the lowest and wettest parts of those forests there occurred, just as there may occur to-day, a large accumulation of fallen trees and other vegetable refuse. In the ordinary way these would simply rot, due to the work of insects and the fungi of decay, and in a few score years there would be nothing to show. “Dust to dust” would be, and is, the history of so many living things that it is only some machinery for arresting this process which will give us very different results. In the case of coal formation the original impetus appears to be certain microscopic organisms, probably saprophytic fungi, fossil remains of which have been identified, which work upon the fallen mass of vegetation and start its decay, but which can only do so while their prey is still within the influence of the air. The initial stages of decay must, therefore, have been going on while the water was low enough for these organisms to work. But in many parts of that ancient landscape the water level was a fluctuating quantity, due to local conditions or to changes in the earth’s crust. So that many times partially decomposed vegetation masses would become submerged, stopping the work of these organisms of decay that demand air, but providing the only conditions under which certain others could complete the transformation. These bacterial organisms that will work only when deprived of air continue the process, but in a different way. For one thing, the lack of air delays decomposition or almost stops it, as witness the resistance of logs under water, some of which are known to be hundreds of years old. And forest stumps off the coast of Cape May, in New Jersey, are in nearly as perfect a state as when first submerged, over 40,000 years ago. In the production of coal these anærobic (living without air) bacteria release oxygen and hydrogen from the partly decayed mass, leaving as a residue a substance known as peat, which is largely carbon. The transformation of peat into coal depends upon requisite pressure of the strata that may be laid down on top of the peat bed, and probably upon chemical changes that go on after