248 DESCBIPTITE CATALOGUE 



distinguished from the surrounding matrix by their different 

 colour — black in a light rock or white in a dark one. 



Brongniart (1828 a) described the genus under the name 

 Facoides in his § Oigartinites as follows (p. 20) : — " Fronde 

 rameuse, a branches presque-cylindriques, charnues, jamais 

 membraneuses." He divided the group into nine species, to 

 the number of which many later writers have added. Much 

 that was said about the fossil Algse as a whole (p. 234, ante) 

 applies particularly to this section, and it does not appear neces- 

 sary to enter into an exhaustive recapitulation of all the "species" 

 described, even among the Cretaceous specimens of Chondrites. 

 In contrast to most of the earlier writers who tended to multiply 

 genera and species of fossil Algge, Ettingshausen (1863) pointed 

 out that a number of the so-called Algae, placed in this genus by 

 Pischer-Ooster and others, cannot be accepted. He also noted 

 the diflflculty of distinguishing between many of the forms to 

 ■which distinct specific names have been given, because of the 

 intermediate stages which occur to connect them. 



In the controversy on the algal nature of fossil Algse, the genus 

 Chondrites is one of the most disputed. Nathorst (1886 a) main- 

 tains that the forms are not algoe and supports this view with 

 ■weighty arguments. Por example, he points out how the very 

 nature of the matrix, particularly in the Flysch deposits, shows 

 that the beds must have accumulated rapidly, -while Algse of the 

 nature of the supposed " Chondrites" do not inhabit troubled 

 waters. He also makes much of the argument that the 

 specimens are not carbonised and sho^w no trace of vegetable 

 substance even when they occur in rocks ■which contain other 

 true vegetable fossils which are carbonised. This objection, 

 ho^wever, seems to be sufficiently answered by the fact that 

 even among living sea^weeds the decay takes place in a different 

 manner from that of the higher plants, owing to the different 

 chemical composition of the plant-body in the t^wo types of 

 vegetation. 



After having read most of the extensive and highly con- 

 troversial literature on the subject, and having seen a large 

 number of specimens in most of the leading museums, my 

 conclusion is that the " genus " Chondrites does contain " species " 

 which are truly the remains of algse, though many of those 

 described for the genus are probably purely physical phenomena. 



