(36) 



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 

 of carboniferous age, showing the transformation of vege- 

 table 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 botan- 

 ical relationship, as the structure of the primitive plants was 

 not well adapted for preservation as fossils. For example, 

 some organisms appear as mere filamentous strips of graphite 

 in white limestone, 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; Dendrophycus, 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 described 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 Lepidoden- 

 dron, Sigillaria and Calamites, and the early seed-bearing 

 plants, the cone-bearers (Gymnosperms), represented by 

 Cordaites, with the fossils under Trigonocarpon, Rhabdo- 

 carpon 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 Cycadofili- 

 cales, that is, plants that had characteristics of both the ferns 

 and the sago-palms, but more closely related to the latter 

 than to the ferns. 



