66 THE APPLICATION OF THE MICROSCOPE 



preserved, in their smallest detail, the structure of the organised 

 body to which they owed their origin. 



In 1840, M. A. Brongniart followed up these investigations 

 and examined many varieties of fossil wood. 



From these and other observations we learn that, generally 

 speaking, the lignites or fossil wood of the Tertiary strata present 

 a tolerably close resemblance to the wood of the present day. 

 Thus the ordinary structure of the dicotyledonous and monocoty- 

 ledonous stems may be discovered in such lignites in the greatest 

 perfection, and the peculiar modification presented by Coniferous 

 wood is also most distinctly exhibited. 



As we descend through the strata of the secondary period, we 

 meet more and more rarely with the ordinary dicotyledonous 

 structure, and the lignites of the earliest deposits of these series 

 are generally either gymnosperms or palms. 



Descending into the Palaeozoic series, we are presented in the 

 vast coal formations with an extraordinary proof of the prevalence 

 of a most luxuriant vegetation in a comparatively early period of 

 the world's history, and the microscope lends the geologist essen- 

 tial assistance, not only in determining the nature of much of that 

 vegetation, but also in demonstrating that coal itself is nothing 

 else than a mass of decomposed vegetable matter, derived from 

 the decay of an ancient vegetation. The determination of the 

 characters of the Ferns, Sigillarise, Lepidodendra, Calamites, etc., 

 whose forms are preserved in the shales which are interposed 

 between the coal strata, has generally been based on their external 

 characters, as it is seldom the internal structure is well enough 

 preserved for microscopical examination, but recently coal-plants 

 have been found in a better state of preservation, whose internal 

 structure has been studied microscopically ; and the careful 

 researches of Professor Williamson have shown that they formed 

 a series of connecting links between the Cryptogamia and flower- 

 ing plants, being allied to the Eqidsetaccce and Lycopodiacecr^ etc., 

 in the character of their fructification, whilst their stem structure 

 foreshadowed both the endogenous and exogenous types of the 

 latter. Even in the coal itself, which presents the appearance of 

 a structureless mass of black carbonaceous matter, there are found 

 a multitude of minute, resinoid, yellowish-brown granules, which 



