cxxxiv BRITISH GRAPTOLITES. 



.1/. Marri, M. Holmi, M. densus, M. Nicholsoni, M. Clingani var. tenera, and 

 var. Hopkinsoni. 



The group of Kamptopodes contains M. nuntius. 



The genns Retiolites is represented by R. perlatus and R. obesvs. 



Ig97 In the year 1897, Walther, of Jena, published in the pages 



Lapworth, of the ' Zeitschrift der deutschen geologischen Gesellschaft ' 



" Die Lebensweise der a memoir on the "Mode of Life of Fossil Sea Animals." 



Graptolithen," in Thig memo j r includes (pp. 238-258) an article by Lapworth 



(ITT , ,. T , . on " The Mode of Life of the Graptolites." In this, Lapworth 



Ueber die Lebensweise ... . 



fossiler Meeresthiere " dealt with this subject in the same comprehensive manner as 



' Zeitsch. d. deutsch. he had already dealt with the classification of the Graptolites 



geol. Gesell.,' vol. xlix, in 1873, and their distribution in 1879-80. 



He adduces the facts known with reference to the relative 



distribution of the Graptolites in the various types of sediment within the British 



Isles, and shows that these facts go to prove that : 



(1) The presence of Graptolites in any of our British rock-layers stands 

 in some way related to the presence of carbonaceous matter in the sediments in 

 which the Graptolites occur. 



(2) Although Graptolites are found in all our Proterozoic sediments, yet they 

 are normally and typically restricted to regions where much carbonaceous matter 

 was deposited. 



(3) The relative abundance of Graptolites in any single layer or rock-group is 

 in some way connected with the calm of the sea-floor where the carbonaceous 

 deposits were laid down (for the material in which the Graptolites lie embedded 

 is usually so impalpable in grain that the gentlest current would have removed it) ; 

 and that the most typical and richest British Graptolite-bearing beds are those 

 which accumulated at the slowest rate. 



It is next shown that the Graptolites themselves did not supply the car- 

 bonaceous matter in the sediments, nor did they live where they are now found. 

 The carbon-producing organisms must also have been strangers to the locality, and 

 it is inferred that these must have been floating sea-weeds. 



The distribution of the black sediments and their thinness both point in the 

 same direction ; they are deposits formed mainly from the relics of floating sea- 

 weeds, arranged in quiet waters parallel to the shore, having been drifted by 

 currents and sinking when waterlogged to the bottom. The presence of Grapto- 

 lites associated with these is in harmony also with the abundance of Hydroid 

 organisms living on the fronds of the Sargassum sea-weed of the present day, 

 which have been drifted from the shore, and become accumulated in special 

 regions of the ocean or swept by currents into almost all latitudes. 



These conclusions being conceded, we have what appears to be the clue to the 

 mode of life and the general line of evolution of the Graptolites, including both 



