CHAPTER XI. 



THE MICROSCOPE IN GEOLOGY (continued). 



IT has long been suspected that the extremely useful 

 substance called coal is nothing else than a con- 

 solidated mass of decomposed vegetable matter ; it 

 is not, indeed, uncommon to find certain markings or 

 indications of a vegetable origin in a lump of coal, 

 and the microscope has enabled us to determine the 

 nature of that vegetation by revealing its structure. 

 It shows us that the coal vegetation was in a great 

 measure coniferous in its nature, "that it probably 

 approximated most nearly to that group of existing 

 Coniferae to which the Araucaria belong." It is one 

 characteristic of coniferous wood to exhibit a number 

 of glandular dots on the woody fibres ; now these 

 glandular dots are often to be seen in sections of coal. 

 Owing to the extreme friability of coal, its examination 

 is attended with some difficulty, for it is no easy 

 .matter to reduce slices to the necessary degree of 

 tenuity. The following mode of examining the 

 structure of coal is taken from the " Micrographic 

 Dictionary:" "The coal is macerated for about a 

 week in a solution of carbonate of potash ; at the end 

 of that time it is possible to cut tolerably thin slices 

 with a razor. These slices are then placed in a watch- 

 glass with strong nitric acid, covered, and gently 

 heated ; they soon turn brownish, then yellow, when 

 the process must be arrested by dipping the whole 

 into a saucer of cold water, or else the coal would 

 be dissolved. The slices thus treated appear of a 

 darkish amber colour, very transparent, and exhibit 

 the structure when existing most clearly. The speci- 



