532 STUDIES IN FOSSIL BOTANY 



4. The Leaves. — The leaves of Cordaites are fossils 

 of frequent occurrence, especially in the Upper Coal- 

 measures, as, for example, at Radstock in Somersetshire, 

 and in the coal-fields of Central France, where they 

 appear to have played an important part in the formation 

 of coal. At St. Etienne, certain beds of coal are said to 

 consist exclusively of dense masses of the carbonised 

 leaves of Cordaiteae. But in addition to the carbonised 

 remains and impressions, which are ill adapted for the 

 investigation of structure, petrified specimens also 

 occur. Thus, in the " black flints " of Grand Croix- 

 silicified remains of Cordaitean leaves are packed 

 together in layers, " like damp Beech-leaves on the 

 ground in our forests." 1 These silicified specimens 

 are often in a state of exquisite preservation, and 

 rendered it possible for the French palaeontologists, 

 notably M. Renault, to work out the structure in great 

 detail. The anatomical specimens hitherto recorded 

 are all referable to the genus Cordaites, though there 

 is often some doubt as to the particular species (as 

 determined from impressions) to which they belonged. 



Broadly speaking, the structure of the leaf of 

 Cordaites resembles that of a single pinna of the leaf of 

 a Cycad, such as Zamia, while there is a more general 

 resemblance to the leaf of Agathis, or one of the 

 larger-leaved Araucarias. There are, as might be 

 expected, appreciable specific differences among the 

 various Cordaitean leaves examined. For example, in 

 the leaf shown in transverse section in Fig. 192, A, 

 referred provisionally to C. angulosostriatus, each of 

 the numerous parallel vascular bundles is enclosed in 



1 Solms-Laubach, Fossil Botany, English edition, p. 105. 



