FOSSIL ALG^. 39 



Nathorst pointed out after obtaining similar markings by 

 experiment that many of them were mere trails of animals 

 and other casual impressions, or the remains of other 

 organisms, and while thus sweeping away an encumbrance 

 of little credit to botanical literature he laid down the useful 

 rule that the claims of no organism of the kind should be 

 accepted unless it exhibit actual structure, or, at all events, 

 a rind of coal. That this excellent rule is somewhat too 

 severely exclusive has been pointed out by Graf zu 

 Solms-Laubach (7), since coal " may entirely disappear 

 in the course of time from remains that are undoubtedly 

 organic, if they are deposited in a porous rock ". A 

 literal application of it would affect many very definite 

 and characteristic impressions of fossil plants, but there 

 is no gainsaying the healthy nature of his conditions. Any 

 departure from them must be supported by strong evi- 

 dence and properly safeguarded by a consideration of 

 the nature of the bed as disclosed by other remains. Un- 

 fortunately the evidence of impressions of outward forms 

 is little to be trusted in the case of Algae, since few 

 groups of them exhibit steadfast and characteristic outlines 

 owing to their extreme plasticity in response to their 

 environment. Nathorst's useful results were strongly dis- 

 puted by the Marquis de Saporta (3), who furnished his 

 own condemnation in the illustrations to his memoir. 

 These examples of astonishing innocence and credulity 

 as to the characteristic forms of Algae are an eloquent 

 plea for the rigorous employment of Nathorst's conditions. 

 (The reader is referred to So\ms-L,a.uba.ch's Fossil Bota7iy (7) 

 and to Zittel's Handbuch der Palceontologie, II. Abth. Palcso- 

 phytologie (8), commenced by Schimper and completed 

 by Schenk, for further details and references to the literature 

 of this portion of the subject.) We are left, then, with a 

 small residuum of organisms, which possess, however, the 

 exceptional interest of being our only known remains of the 

 vegetation of past oceans, their shore Algae and their plant 

 Plankton. 



The great number of Algae existing at the present day, 

 their variety of form and range of habitat, would lead one to 



