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To the left in an area that was once Whittlesea Mere and there is a pile of Bog Oak that has been pulled to the surface and in the corner of a Farmer's field. It is not like normal wood, but a cross between wood and coal, and cannot be cut with an ordinary saw, no more that coal can be cut with a hand saw. The question is, how and why it is brought to the surface? It is common practice for farmers to deep plough these fields to try and bring nourishment in the peat to the surface. Owing to peat shrinkage, these Bog Oaks are often caught by a plough, and are therefore a nuisance to the farmer, who pulls them to surface of the land, and places them in a pile. This is not a common sight nowadays, as most of the Bog Oaks have already been pulled to the surface, as peat is shrinking slower. -- Geography and Geology of Fens Agriculture, Natural History, Food Growing and Roman and Saxon History

...It is not like normal wood, but a cross between wood and coal, and cannot be cut with an ordinary saw, no more that coal can be cut with a hand saw...
One of a number of trees of the 'petrified forest' North of Lake Qaruninth, Egypt.
Lesvos, Greece.
The rapid covering of tree trunks, branches, and leafs lead to isolation from atmospheric conditions. Along with the volcanic activity, hot solutions of silicon dioxide penetrated and impregnated the volcanic materials that covered the tree trunks. Thus the major fossilisation process started with a molecule by molecule exchange of the organic plant by inorganic materials. In the case of the Petrified forest of Lesvos, the fossilisation was perfect due to favourable fossilisation conditions. Therefore morphological characteristics of the tree trunks such as the annual rings, barkers, as well as the internal structure of the wood, are all preserved in excellent condition.
METASOMATISM.
METASOMATISM (Gr. Aera, change, QW / .(a, body), in petrology, a process of alteration of rocks by which their chemical composition is modified, new substances being introduced while those originally present are partly or wholly removed in solution.
The agencies of metasomatism are in nearly all cases aqueous solutions; probably they were often at a high temperature, as metasomatic changes are especially liable to occur in the vicinity of igneous intrusions (laccolites, dikes and necks) where large quantities of water were given off by the volcanic magma at a time when it had solidified but was not yet cold. Metasomatism also usually goes on at some depth, so that we may readily believe that it is favoured by increase of pressure...

Petrology=petrified trees?