The investigation of silicified specimens has, in the hands of Renault, yielded striking results.
At a more recent horizon, the silicified specimens of the Mesozoic Gymnosperms from Great Britain, France, and especially North America, are no less important.
Calcified specimens are especially characteristic of the British Carboniferous formation; their preservation is equally perfect with that of the silicified fossils, and their investigation by Witham, Binney, Williamson and others has proved no less fertile.
Logani the stem, which is found in a silicified state, may be as much as 3 ft.
The first evidence for the existence of Palaeozoic Bacteria was obtained in 1879 by Van Tieghem, who found that in silicified vegetable remains from the Coal Measures of St Etienne Bacteria.