REPORT OP THE DIRECTOR I919 t2^ 



guished three species among them, as they prove to be of considerable 

 value for the differentiation of horizons. 



The general succession of the graptolite zones is strikingly alike 

 in all parts of the w^orld, as pointed out by the writer in the Grap- 

 tolites of New York, that is, the succession is everywhere, in 

 ascending order : 



1 Beds with Dictyonema flabelliforme 



2 Clonograptus and Dichograptus horizons 



3 Tetragraptus horizons 



4 Didymograptus horizons 



5 Phyllograptus horizons 



6 Nemagraptus horizon 



7 Horizons with Qimacograptus and Diplograptus 



This succession is distinctly a phylogenetic one, as far as the series 

 from Dictyonema through Clonograptus, Dicho- 

 graptus, Tetragraptus to Didymograptus is con- 

 cerned. Likewise Phyllograptus and Nemagraptus 

 are later aberrant branches enjoying a brief period of ascendency; 

 and the development of the Axonophora, as represerited by 

 Climacograptus and Diplograptus is an important, 

 new departure of the graptolites in the Middle Ordovician. 



The recent investigations of Raymond in Quebec (op. cit., 1914) 

 and of McLearn^* ^n New Brunswick seem to bring out the inter- 

 esting fact that differences in the succession and development of 

 the graptolite zones are already observable between New York and 

 Quebec and New Brunswick; for the lowest Didymograptus zone 

 does not appear to be nearly so well developed at Levis as at the 

 Deep Kill, and most of the large specimens of the " horizontal " 

 species of Didymograptus are, at Levis, found in the subzone of 

 Didymograptus bifidus (Raymond, op. cit., p. 528). 

 McLearn (op. cit., p. 55) came even to the conclusion, that " the 

 faunas all show greater affinity with those of northwestern Europe, 

 especially with the Lake District of England and St Davids at 

 Caermarthenshire, Wales, than with Quebec and New York faunas." 

 In both Canadian localities the earlier appearance of the important 

 zone graptolite Didymograptus bifidus is especially notable. 

 Whether this is due to a longer persistence there of the horizontal 

 Didymograpti, or an actual earlier appearance of the guide-fossil of 

 the zone ; it indicates differences in the composition of the zones due 



"F. H. McLearn. The Lower Ordovician (Tetragrapus zone) at St 

 John, New Brunswick, and the new genus Protistograptus. Amer. Jour. 

 Sci., 4o : 49. 1915. 



