INTRODUCTION 



The carbonaceous material in these analyses is speci- 

 ally interesting, because it represents the actual tissue 

 preserved in the petrifaction. In some silicious speci- 

 mens, however, the organic substance has entirely 

 perished, and the cell-walls are represented by a system 

 of minute crevices in the matrix. Though all the 

 essential features of the structure may be thus marked 

 out, they may still be very difficult to see. In such 

 cases M. Renault made use of stains, by which the 

 cracks representing the cell-walls were injected. He 

 thus obtained a coloured image of the structure, and 

 so for the first time succeeded in staining a fossil 



1 Taken together with all the inorganic residues. 



2 The figures are practically percentages, according to weight. The first 

 two columns give the analyses of "coal-balls" from the Lower Coal- 

 measures of Lancashire. The third column relates to the plant -bearing 

 calcareous deposit near Burntisland, in Scotland, at a much lower horizon. 

 The most important variation is in the amount of Magnesium Carbonate, 

 which in many of the coal-balls is nearly equal to that of the Calcium 

 Carbonate. 



