REPORT OF THE STATE PALEONTOLOGIST 1901 557 



the other species are represented in the latter only by dwarfed, 

 mutations. The term " Tetragraptus zone ", which has been 

 proposed for the corresponding zone in the Skiddaw beds of 

 England, appears, therefore, to be also quite appropriate for 

 the American graptolite zone. 



Among the species of Didymograptus it is a striking phe- 

 nomenon that only the forms with horizontally extended' 

 branches are present, while the " tuning fork " species, so char- 

 acteristic of the middle Lower Siluric zones of Europe, are still) 

 entirely absent. Goniograptus thureaui also extends^ 

 into the next zone, but does not there attain the size of its 

 ancestors. The genus Phyllograptus attains its largest size 

 (Ph. typus) and its greatest number of species only in the 

 next horizon. 



Nearly all the species of this fauna, which bear Hall's name^ 

 as that of their author, were described^ as coming from the^ 

 " shales of the Quebec group, Point Levis." While Hall in these^ 

 important papers did not enter on a discussion of the age of the 

 graptolite shales of the Quebec group, he correlated, in the table 

 showing the vertical distribution of the graptolites (loc. cit. p. 55),. 

 the Quebec group with the Calciferous and Chazy periods, thus 

 placing these graptolite beds in a general way near the base 

 of the Lower Siluric. Nor did he attempt to separate the grap- 

 tolite fauna of the Quebec group into its constituent zonal 

 faunules, but from the associations which he mentions in the- 

 descriptions of the species the presence of two different faunas, 

 that of Point Levis and that of the St Anne river, is clearly 

 apparent. These two faunas were differentiated as the Point 

 Levis zone and the Kiver St Anne zone by Lapworth,^ and the^ 

 latter zone, in accordance with the succession established in 

 England, is placed above the former. 



Later, the same distinguished investigator of the graptolites 

 studied^ collections from the lower paleozoic rocks on the soutb 



'Geol. sur. Canada. Rep't for 1857; and fig. and descr. Can. org. rom. 

 Decade 2. 1865. 

 'Ann. and mag. nat hist. 1880. 5th ser. 5:275. 

 'Roy. soc. Canada. Proc. and trans. 1886. 4:167 ff. 



