7T2 MICROSCOPIC STRUCTURE OF COAL. 



exhibit the characters of the woody structure extremely well, when 

 mounted in Canada balsam. — Generally speaking, the Lignites of 

 the Tertiary strata present a tolerably close resemblance to the 

 Woods of the existing period ; thus the ordinary structure of Dico- 

 tyledonous and Mouocotyledonous Stems may be discovered in 

 such lignites in the utmost perfection ; and the peculiar modifica- 

 tion presented by Coniferous wood is also most distinctly exhibited 

 (Fig. 216). As we descend, however, through the strata of the 

 Secondary period, we more and more rarely meet with the ordinary 

 Dicotyledonous structure ; and the Lignites of the earliest deposits 

 of these series are, almost universally, either Gymnosperms* or 

 Palms. 



586. Descending into the Palaeozoic series, we are presented 

 in the vast Coal formations of our own and other countries with an 

 extraordinary proof of the prevalence of a most luxuriant Vegeta- 

 tion in a comparatively-early period of the world's history; and 

 the Microscope lends the Geologist essential assistance, not only in 

 determining the nature of much of that vegetation, but also in 

 demonstrating (what had been suspected on other grounds) that 

 Coal itself is nothing else than a mass of decomposed Vegetable 

 matter, chiefly derived from the decay of Coniferous wood. The 

 determination of the characters of the Ferns, Sigillarice, Lepido- 

 dendra, Catamites, and other kinds of vegetation whose forms are 

 preserved in the Shales or Sandstones that are interposed between 

 the strata of Coal, must be chiefly based on their external charac- 

 ters ; since it is very seldom that these specimens present any 

 such traces of minute internal structure as can be subjected to 

 Microscopic elucidation. But notwithstanding the general absence 

 of any definite form in the masses of decomposed Wood of which 

 Coal itself consists (these having apparently been reduced to a 

 pulpy state by decay, before the process of consolidation by pressure, 

 aided perhaps by heat, commenced), the traces of structure revealed 

 by the Microscope are often sufficient — especially in the ordinary 

 'bituminous' Coal — not only to determine its Vegetable origin, 

 but in some cases to justify the Botanist in assigning the characters 

 of the vegetation from which it must have been derived. Different 

 specimens of Coal exhibit these structural characters in very 

 different degrees of distinctness ; but they uniformly indicate, with 

 a clearness proportionate to their distinctness, that such vegetation 

 must have been Coniferous in its nature, and that it probably 

 approximated most nearly to that group of existing Coniferae to 

 which the Araucarice belong. These inferences are based upon 

 the fact that the Woody structure consists of Woody Fibres without 

 interposed Vessels ; upon the presence of 'glandular' dots on the 

 woody fibres; and upon the peculiar arrangement of these dots in 

 two or more rows, alternating one with another (§§ 294, 301). — 



* Under this head are included the Cycadca>, along with the ordinary 

 Cbnifera or Tine and Fir tribe. 



