106 DIFFICULTIES AND SOURCES OF ERROR. [CH. 



I'homme^, represents a fern-like fossil on the surface of a piece 

 of Silurian slate. The supposed plant was named Eopteris 

 Morierei Sap., and it is occasionally referred to as the oldest 

 land plant in books of comparatively recent date. In the 

 Museum of the School of Mines, Berlin, there are some specimens 

 of Angers slate on some of which the cleavage face shows a 

 shallow longitudinal groove bearing on either side somewhat 

 irregularly oblong and oval appendages of which the surface is 

 traversed by fine vein-like markings. A careful examination 

 of the slate reveals the fact that these apparent fern pinnules 

 are merely films of iron pyrites deposited from a solution which 

 was introduced along the rachis-like channel. Many of the 

 extraordinary structures described as plants by Reinsch'' in his 

 Memoir on the minute structure of coal have been shown to be 

 of purely mineral origin. 



The innumerable casts of animal-burrows and trails as well 

 as the casts of egg-cases and various other bodies, which have 

 been described as fossil algaj, uiust be included among the most 

 fruitful sources of error. 



It requires but a short experience of microscopical in- 

 vestigation of fossil plant structures to discover numerous 

 pitfalls in the appearance presented by sections of calcareous 

 and siliceous nodules. The juxtaposition of tissues apparently 

 parts of the same plant, and the penetration by growing roots 

 of partially decayed plant debris, serve to mislead an unpractised 

 observer. In sections of the English ' calcareous nodules ' 

 one very frequently finds the tissue of Stigmarian appendages 

 occupying every conceivable position, and preserved in places 

 admirably calculated to lead to false interpretations. The more 

 minute investigation of tissues is often rendered difficult by 

 deceptive appearances simulating original structures, but which 

 are in reality the result of mineralisation. It is no easy matter 

 in some cases to discover whether a particular cell in a fossil 

 tissue was originally thick-walled, or whether its sclerous 



^ Saporta (79) (77). Eopteris is included among the ferns in Sohimper and 

 Sehenk'a volume of Zittel's Handbuch der Palaeontologie (p. 115), and in some 

 other modern works. 



' Eeiusoh (81). 



