348 E. Billings on the Graptolites of the Lower Silurian. 



Flags at the Stiper Stones, the true Primordial Zone as recognized 

 in England.* G. geminus as I understand occurs in Sweden in 

 the upper part of the Lower Silurian. G. pristis ranges through 

 the whole formation in different countries, and I believe that 

 G. MurcMsonii has a similar extended vertical distribution. A 

 species occurs in the slates of the Quebec group which is clearly 

 allied if not identical with G. geminus. On comparing the 

 works of the different authors it will be seen that other species 

 are identified as having not only a great geological but a wide 

 geographical range. It would appear thus that graptolites cannot 

 always be relied upon to show that exposures of rock widely sepa- 

 rated from each other are either of a different or of the same age. 



In the Primordial Zone of Bohemia no graptolites have been 

 discovered. Of the genus Dictyontma one species D. sociale 

 (Salter) occurs in the Lingula Flags in England, but none of the 

 ordinary graptolites have (unless very recently) been observed in 

 that formation. In Sweden Dictyonema flabelliformis and agrap- 

 tolite which Barrande says has " an appearance analogous to that 

 of G. pristis'^ occurs in the slates of Andrarum, in Angelins 

 Regio B. in the true Primordial Zone. It would appear from 

 all this that graptolites are rare in the Primordial Zone and that 

 they abound in every stage of the second Fauna being most nu- 

 merous in slaty rocks and rare in limestones and sandstones, f 



As to their value in identifying strata Barrande observes that 

 as " in general they consist of forms very similar in appearance 

 it is difficult to distinguish them especially when found in frag- 

 ments. The study of the family is not sufficiently advanced to 

 enable us to recognise with certainty among its types those which 

 may characterise exclusively each one of the three faunae of the 

 Silurian. "J 



I have prepared the above observations in order to show that 

 the occurrence of graptolites in rocks so ancient as those of the 

 Quebec group is not inconsistent with what we know of their geo- 

 logical range in other countries and consequently that we are not 

 compelled to refer all the slates in which they are found in North 

 America to the Hudson Biver group. 



* See Sir R. I. Murchison's 3rd Ed. of Siluria, pp. 39. 50. * 



t See Barrande's Parallele entre les depots Siluriens de Scandinavie et 



de Boheme, p. 44. And also ANGELi>fS " Palceontologia Scandinavicay" 



p. IV. 



t Documens anciens et nouveaux sur la fauna primoi'diale et le systeme 



Taconique en jimSrique, par M. J. Barrande, Bui. Geo. Soc. France. 



2e Series, Vol. 18, p. 288. 



