It will not be amiss, in this place, to give a short detail of such bodies as are capable of either being petrified themselves, or of leaving their impressions in stony matter. By being petrified, is meant being impregnated with stony, pyritical, or any other metalline or sparry matter; for there are inumerable specimens, wherein all these are apparent. TESTACEOUS _and_ CRUSTACEOUS ANIMALS. The shelly matter of these is of so compact and dry a nature, that they will endure for ages: and if in a soil or bed where moisture has access, they will receive stony matter into their pores, and become ponderous in proportion to the quantity imbibed. If in a dry place, they will remain fair and sharp, suffering very little change by any length of time; whilst the flesh of these, being subject to putrifaction, is soon destroyed; and yet, according to circumstances that happen, some of these may be replaced in due form by stony particles. I have a gryphites, with the form of the fish in its place, as is the case in several of the oyster kinds. This may be occasioned by the shells being close, or nearly so, and stony matter gradually insinuating into their cavity, so as to fill up the whole. WOOD. The kinds of wood found fossil are very different: some are of a firmer texture than others: and this too is according to the places wherein they are deposited. Some I have seen so highly impregnated with a fine stony and pyritical matter, as to bear a polish like a pebble; some, tho’ quite reduced to stone, yet preserving the fibrous appearance of the original state; and some which is found in boggy bottoms, being not at all changed, except in color: this is called bog oak, or bog deal, well known to country people in many places of these three kingdoms, who light themselves about their business with slips of this wood, cut on purpose instead of candles, as it burns with a clear and durable flame. It is remarkable, that altho’ oak or fir shall lie ages immersed in water under ground, it shall not putrify; but acquire such sulphureous particles by lying in steep, in the bog-water, as to qualify it for this use. Other wood, deposited in marly ground, is found incrusted over, trunk and branches, with a white crust; the wood remaining intire within. At other times, wood thus incrusted shall be eroded by the matter which covers it, having something acrimonious in its substance. We may add to these, clusters of the twigs of shrubs, and small wood, which we find flakes of, incrusted with sparry or calcarious matter, in many places; parts of which are totally changed into that matter, whilst others are only inveloped with it. BONES _of_ ANIMALS.