FOSSIL PLANTS. 45 



determine the order of treatment of the matter passed 

 in review. 



Any additions to our knowledge of the floras of pre- 

 coal-measure times are especially valuable : their value is 

 increased by the fact that we are still very ignorant of 

 the true nature of the vegetation, anterior to the Upper 

 Carboniferous period, and also because of the great import- 

 ance of extending our retrospect as far back as possible 

 towards the earliest phases of plant evolution. 



The list of undoubted fossil plants from strata older 

 than the Devonian period is an exceedingly small one. 

 In the case of the earliest records of plant fossils there are 

 always certain forms which are of no botanical value, and 

 which have little or no claim to occupy a place in the vege- 

 table kingdom. 



Since 1878, the genus Glyptodendron of Claypole 1 has 

 frequently been quoted as a Silurian plant, resembling 

 a Lepidodendron in its surface markings. Now it appears 

 we may consider Claypole's genus as in all probability 

 a fragment of a Silurian Cephalopod, and not a plant. 

 This conclusion has been arrived at by Mr. Foerste 2 

 after a thorough examination of the type specimen, and a 

 comparison of it with some Cephalopods from the Clinton 

 limestone which have certain surface markings apparently 

 identical with the "scars" of Glyptodendron. Strong con- 

 firmation of these views is expressed in a footnote by 

 Claypole, who considers that Foerste has made out a good 

 case against the existence of fossil plants of Clinton age in 

 Ohio. 



In recent years the microscopic examination of sedi- 

 mentary rocks has been to a certain extent revived, and 

 some of the results obtained are of great interest with 

 regard to the part played by vegetable organisms in the 

 process of rock- building. Mr. Wethered's researches have 



1 Geo/. Mag., Dec, ii., vol. v., 1878, p. 558. 



2 American Geologist, vol. xii., 1893, p. 133. Mr. A. H. Foord tells 

 me that the Glyptodendron-Y\\uz pattern represented by Foerste on the 

 Crytoceras must be some encrusting foreign matter, and not a part of 

 the Cephalopod shell. 



