(50) 



Cambrian, Lower Silurian, Upper Silurian, Devonian and 

 Carboniferous Periods. In floor- and wall-case No. I are 

 specimens of graphite of eozoic age and of anthracite and 

 bituminous coal or carboniferous age, showing the trans- 

 formation of vegetable matter into the ultimate condition 

 of pure carbon in the form of graphite or "black lead" 

 in the oldest rocks. Other specimens in this case, classed 

 as algae, are of uncertain botanical relationship, as the 

 structure of the primitive plants was not well adapted for 

 preservation as fossils. For example, some organisms ap- 

 pear as mere filamentous strips of graphite in white lime- 

 stone, without any trace of the original structure remaining, 

 while others may be seen as casts and impressions which 

 closely simulate in general appearance different parts of 

 the seaweeds now existing. In this series of problematic 

 fossils are also included a number of forms at one time 

 definitely classed as plants but now by some assumed to 

 be of animal or inorganic origin; namely, Scolithus, which 

 may be caused by worm burrows; Phytopsis, which may 

 be a coral; Plumalina, which may be a hydroid; Dendro- 

 phycus, which may be current-markings; and Dictyolites, 

 which are most likely sun-cracks. All of these, however, 

 have at one time or another been definitely regarded as 

 the remains of marine plants and were originally so de- 

 scribed and classified. 



In these cases and in wall-case No. 2 are also the remains 

 of the earliest fern-plants and their allies (Pteridophyta) 

 of Devonian and Carboniferous age, represented by 

 Lepidodendron, Sigillaria and Catamites, and the early 

 seed-bearing plants, the cone-bearers (Gymnosperms), 

 represented by Cordaites, with the fossils under Trigono- 

 carpon, Rhabdocarpon and other genera. 



Floor-cases Nos. 2 and 3 and wall-case No. 3 contain 

 specimens of Carboniferous age, for the most part ferns or 

 fern-like plants, which were originally described as ferns, 

 but which are now placed in a different group, the Cycado- 

 filicales, that is, plants that had characteristics of both 



