Professor Buckland, in his _Bridgewater Treatise_, speaking of the impressions of plants found in the coal mines, says; "The finest example I have ever witnessed is that of the coal mines of Bohemia. The most elaborate imitations of living foliage upon the painted ceilings of Italian palaces bear no comparison with the beauteous profusion of extinct vegetable forms with which the galleries of these instructive coal mines are overhung. The roof is covered as with a canopy of gorgeous tapestry, enriched with festoons of most graceful foliage, flung in wild irregular profusion over every part of its surface. The effect is heightened by the contrast of the coal-black colour of these vegetables with the light ground-work of the rock to which they are attached. The spectator feels himself transported, as if by enchantment, into the forests of another world; he beholds trees, of forms and characters now unknown upon the surface of the earth, presented to his senses almost in the beauty and vigour of their primeval life; their scaly stems and bending branches, with their delicate apparatus of foliage, are all spread forth before him, little impaired by the lapse of countless ages, and bearing faithful records of extinct systems of vegetation which began and terminated in times of which these relics are the infallible historians." [Verse: "Surely every man walketh in a vain show; surely they are disquieted in vain: he heapeth up riches, and knoweth not who shall gather them."--PS. XXXIX.] 274. _What are the chemical components of coal?_ They consist of _carbon_, _hydrogen_, _oxygen_, and _nitrogen_. The proportions of these elements vary in different kinds of coal. Carbon is the chief component; and the proportions may be stated to be, generally, _carbon_, 90 per cent.; _hydrogen_, from 3 to 6 per cent.; the other elements enter into the compound in such small proportions, that, for all ordinary purposes, it is sufficient to say that coal consists of _carbon_ and _hydrogen_, but chiefly of _carbon_. 275. _What is charcoal?_ Charcoal consists almost entirely of _carbon_. It is made from _wood_ by the application of heat, without the admission of air. The hydrogen and oxygen of the wood are expelled, and that which remains is charcoal, or _carbon_ in one of its purest states. 276. _What is animal charcoal?_ Animal charcoal, like vegetable charcoal, consists of _carbon_ in a state approaching purity. It is made from the _bones of animals_, heated in iron cylinders. It is commonly called _ivory black_. 277. _What is the purest form of carbon known?_ The purest form of _carbon_ is the _diamond_, which may be said to be absolutely pure.