148 THALLOPHTTA. [CH. 



main divisions of the algae are represented among the Flysch 

 Fucoids, but considers that the Phaeophyceae are the most 

 numerous. 



Rothpletz's work is chiefly interesting as illustrating the 

 application of microscopic examination and chemical analysis to 

 the determination of fossil algae. Although he makes out a 

 good case in favour of restoring many of the Tertiary fossils to 

 the plant kingdom, the material at his disposal does not admit 

 of satisfactory botanical diagnosis. 



No doubt some of the fossils from the Silurian and Cambrian 

 rocks are true algae, and Nathorst has pointed out that such a 

 species as Hall's Spheiiothallus angustifolius^ may well be an alga. 

 Additional examples might be quoted from Bornemann and 

 other writers, but in view of the attempts which are sometimes 

 made to trace the development of more recent plants to more 

 than doubtful Lower Palaeozoic Algae, one must agree with 

 Nathorst's opinion, — ''Je crois que Ton rend un bien mauvais 

 service a la th^orie de revolution, en essayant de baser I'arbre 

 gen^alogique des algues fossiles sur des corps aussi douteux 

 que les Bilobites, Crossochorda, Eophyton, etc.''" 



There are many carbonaceous impressions on rocks of 

 different ages which it is reasonable to refer to algal origin, 

 and although such are of little or no botanical value, it may be 

 a convenience to refer to them under a definite term. The 

 comprehensive generic name Algites' has been suggested as 

 a convenient designation for impressions or casts which are 

 probably those of algae. 



Some of the fossils described by Mr Kidston from British 

 Carboniferoiis rocks as probably algae present an undoubted 

 algal appearance, and might be placed in the genus Algites; 

 but in some cases — e.g. Chondrites plumosa^ Kidst. from the 

 Calciferous Sandstone of Eskdale, one feels much more doubtful ; 

 in this particular instance the impressions suggest the fine 

 roots of a water-plant. 



' Hall (47) PL Lxviii. 1 and 2, p. 261. 

 " Nathorst (83) p. 453. 

 ' Seward (942)' p 4_ 



* Kidston (83) PI. xxxii. fig. 2. Specimens of this form may be seen in the 

 British Museum collection. 



